Optical fiber pressure sensor guidewire

ABSTRACT

In an example, this document discloses an apparatus for insertion into a body lumen, the apparatus comprising an optical fiber pressure sensor. The optical fiber pressure sensor comprises an optical fiber configured to transmit an optical sensing signal, a temperature compensated Fiber Bragg Grating (FBG) interferometer in optical communication with the optical fiber, the FBG interferometer configured to receive a pressure and modulate, in response to the received pressure, the optical sensing signal, and a sensor membrane in physical communication with the FBG interferometer, the membrane configured to transmit the received pressure to the FBG interferometer.

This application is related to (1) U.S. Provisional Application No.61/791,486 entitled, “OPTICAL FIBER PRESSURE SENSOR GUIDEWIRE” to Eberleet al. and filed on Mar. 15, 2013, and to (2) U.S. ProvisionalApplication No. 61/753,221, entitled, “OPTICAL FIBER PRESSURE SENSORGUIDEWIRE” to Eberle et al. and filed on Jan. 16, 2013, and to (3) U.S.Provisional Application No. 61/709,781, entitled, “OPTICAL FIBERPRESSURE SENSOR GUIDEWIRE” to Eberle et al. and filed on Oct. 4, 2012,and to (4) U.S. Provisional Application No. 61/659,596, entitled,“OPTICAL FIBER PRESSURE SENSOR GUIDEWIRE” to Eberle et al. and filed onJun. 14, 2012, and to (5) U.S. Provisional Application No. 61/651,832,entitled, “OPTICAL FIBER PRESSURE SENSOR GUIDEWIRE” to Eberle et al. andfiled on May 25, 2012, the entire content of each being incorporatedherein by reference in its entirety, and the benefit of priority of eachis claimed herein.

TECHNICAL FIELD

This document pertains generally to pressure sensing devices and methodsand, in particular, to pressure sensing devices and methods usingoptical elements and techniques.

BACKGROUND

U.S. Patent Application Publication No. 2009/0180730 to Foster et al. isdirected toward a device for sensing an acoustic signal. The deviceincludes a flexible portion including a laser active region having anemitted wavelength that varies according to a mechanical force acting onthe flexible portion, and including a flexible support member operableto flex or bend according to the acoustic signal. The flexible portionis coupled with the support member so as to cause the flexible portionto flex or bend in accordance with the support member, thereby changingthe emitted wavelength of the laser active region of the flexibleportion.

U.S. Pat. No. 7,680,363 to Wakahara et al. (“Wakahara”) is directedtoward an optical fiber pressure sensor capable of detecting a moreminute pressure change. A base film is formed with a through holepassing through first and second surfaces. An optical fiber is fixed tothe base film at a region other than the Fiber Bragg Grating (FBG)portion, such that the FBG portion is positioned on the through hole inplan view. The optical fiber pressure sensor is attached to an objectbody such that the second surface of the base film is closely attachedto a surface of the object body directly or indirectly.

Overview

The present applicant has recognized, among other things, that otherapproaches to pressure sensing guidewires exhibit mechanical performancesuitable for diagnostic assessment of coronary obstructions, buttypically are not suitable for delivery of therapeutic devices. Thepresent applicant has recognized that the other pressure sensingtechnology, namely piezoresistive or piezocapacitive silicon pressuresensors, and associated electrical cables, are relatively large comparedto the size of the components of a typical therapy delivering guidewire.The present applicant has recognized that the incorporation of suchother pressure sensing technology into a coronary guidewiresubstantially restricts the design of the mechanical components of theguidewire and results in significant compromises to the mechanicalperformance. The present applicant has recognized that a smallerpressure sensing technology, when incorporated into a contemporarycoronary guidewire, would be advantageous in restoring the requiredmechanical performance requirements.

Optical fiber technology can be used in pressure sensors for oildiscovery and production, as well as in larger diagnostic catheters forpatients. The present applicant has recognized that telecommunicationindustry standard optical fiber would be too large to incorporate intohigh performance coronary guidewires. Accordingly, the present applicanthas recognized, among other things, that miniaturization of the opticalfiber and optical fiber based pressure sensor presents both a majorchallenge and a major advantage for incorporation into a coronaryguidewire while minimizing the impact on the mechanical performance ofthe guidewire.

The present applicant has recognized, among other things, that theintrinsic sensitivity of an optical fiber sized for insertion into abody lumen may not be sufficient to generate an easily detectable signalwithin the range of pressures associated with a patient. The presentapplicant has recognized that miniaturization of the optical fiber canimpart more flexibility into the fiber. This can be used to mechanicallyenhance the sensitivity of the fiber to pressure, such as with anextrinsic arrangement. The present applicant has recognized that usingFiber Bragg Gratings in the miniaturized optical fiber can provide ahighly cost effective and readily manufacturable design. In addition,the present applicant has recognized that one or more other factors—suchas the temperature coefficient of one or more Fiber Bragg Gratings(FBGs)—can be significantly higher than the intrinsic pressuresensitivity of the optical fiber. As such, a small drift in temperaturewithin a patient can appear as a large pressure change artifact, which,in the context of pressure sensing, is unwanted and likely notacceptable due to the need for accurate pressure measurements.Accordingly, the present applicant has recognized, among other things,that it can be advantageous to provide an optical fiber pressure sensorguidewire that can include temperature calibration, compensation, orcorrection for an optical fiber pressure sensor, such as a Fiber BraggGrating (FBG) arrangement for sensing pressure within a body lumen.

In one example, the disclosure is directed to an apparatus for insertioninto a body lumen. The apparatus comprises an optical fiber pressuresensor comprising an optical fiber configured to transmit an opticalsensing signal, an ambient temperature compensated Fiber Bragg Grating(FBG) interferometer in optical communication with the optical fiber,the FBG interferometer configured to receive a pressure and modulate, inresponse to the received pressure, the optical sensing signal, and asensor membrane in physical communication with the FBG interferometer,the membrane configured to transmit the received pressure to the FBGinterferometer.

This overview is intended to provide an overview of subject matter ofthe present patent application. It is not intended to provide anexclusive or exhaustive explanation of the invention. The detaileddescription is included to provide further information about the presentpatent application.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numeralsmay describe similar components in different views. Like numerals havingdifferent letter suffixes may represent different instances of similarcomponents. The drawings illustrate generally, by way of example, butnot by way of limitation, various embodiments discussed in the presentdocument.

FIG. 1 is a cross-sectional side view illustrating generally, by way ofexample, but not by way of limitation, an example of an FBG pressuresensor in an optical fiber.

FIG. 2 is a cross-sectional side view illustrating generally, by way ofexample, but not by way of limitation, an example of an FBG gratinginterferometer sensor.

FIG. 3 is a conceptual diagram illustrating various exampleconfigurations FBG of an optical fiber pressure sensor, in accordancewith this disclosure.

FIGS. 4A-4C depict various conceptual response diagrams related to theconceptual diagram of FIG. 3.

FIG. 5 is a block diagram of an example of an ambient temperaturecompensation technique in accordance with this disclosure.

FIG. 6A is a block diagram of an example of a laser tracking system, inaccordance with this disclosure.

FIG. 6B is a block diagram of an example of a temperature compensationtechnique in accordance with this disclosure.

FIGS. 7A-7C depict an example of a pressure sensor that can be used toimplement various techniques of this disclosure.

FIGS. 8A-8C depict another example of a pressure sensor that can be usedto implement various techniques of this disclosure.

FIGS. 9A-9C depict another example of a pressure sensor that can be usedto implement various techniques of this disclosure.

FIGS. 10A-10D depict another example of a pressure sensor that can beused to implement various techniques of this disclosure.

FIG. 11 depicts a conceptual response diagram related to the example ofa pressure sensor shown in FIG. 10D.

FIGS. 12A-12C depict another example of a pressure sensor that can beused to implement various techniques of this disclosure.

FIGS. 13A-13C depict an example of a guidewire in combination with anoptical fiber pressure sensor, in accordance with this disclosure.

FIGS. 14A-14C depict another example of a guidewire in combination withan optical fiber pressure sensor, in accordance with this disclosure.

FIGS. 15A-15C depict another example of a guidewire in combination withan optical fiber pressure sensor, in accordance with this disclosure.

FIG. 16 depicts another example of a pressure sensor that can be used toimplement various techniques of this disclosure.

FIG. 17 depicts another example of a pressure sensor that can be used toimplement various techniques of this disclosure.

FIG. 18 depicts another example of a pressure sensor that can be used toimplement various techniques of this disclosure.

FIG. 19 depicts another example of a pressure sensor that can be used toimplement various techniques of this disclosure.

FIG. 20 depicts another example of a pressure sensor that can be used toimplement various techniques of this disclosure.

FIGS. 21A-21D depict another example of a guidewire in combination withan optical fiber pressure sensor, in accordance with this disclosure.

FIG. 22 depicts an example of a combination of a guidewire with anoptical fiber pressure sensor and an imaging sensor, in accordance withthis disclosure.

FIGS. 23A-23B depict another example of a guidewire in combination withan optical fiber pressure sensor, in accordance with this disclosure.

FIG. 24 shows an example of a portion of a concentric pressure sensorassembly.

FIG. 25 shows an example of the pressure sensor assembly as it can beprefinished and included or otherwise incorporated into a percutaneousintravascular guidewire assembly.

FIG. 26 shows an example illustrating how components of the pressuresensor assembly can be integrated into or otherwise incorporated into apercutaneous intravascular guidewire assembly.

FIG. 27 shows an example in which components of the pressure sensingassembly can be retrofitted to or otherwise integrated into an existingguidewire assembly.

FIG. 28 shows an example in which the pressure sensor assembly (e.g., asexplained herein) can be located at a distal end of a guidewireassembly.

FIG. 29 shows an example of a proximal region of a guidewire assembly,such as one of the various guidewire assemblies described herein,terminating at a proximal end connector.

FIG. 30 depicts a conceptual response diagram illustrating the effect ofan uncorrected locking level on a locking wavelength.

FIG. 31 depicts the conceptual response diagram of FIG. 30 compensatedfor optical insertion loss in an optical pressure sensor using varioustechniques of this disclosure.

FIG. 32 is a flow diagram illustrating an example of a method forcompensating for optical insertion loss in an optical pressure sensorusing various techniques of this disclosure.

FIG. 33 is a block diagram of an example of a portion of the lasertracking system of FIG. 6A for compensating for optical insertion lossin an optical pressure sensor using various techniques of thisdisclosure, in accordance with this disclosure.

FIG. 34 depicts a conceptual response diagram illustrating undesirableoptical resonances caused by additional reflection in an optical system.

FIG. 35 depicts the conceptual response diagram of FIG. 34 furtherillustrating undesirable locking circuit wavelength hopping.

FIG. 36 depicts the conceptual response diagram of FIG. 35 compensatedfor optical cavity noise using various techniques of this disclosure.

FIG. 37 depicts a flow diagram illustrating an example of a method forcompensating for optical cavity noise in an optical pressure sensorusing various techniques of this disclosure.

DETAILED DESCRIPTION

Before or during an invasive medical procedure, it can be desirable fora clinician, e.g., a physician, to take one or more pressuremeasurements from within a body lumen of a patient, e.g., a bloodvessel, such as an artery or vein. For example, before implanting astent at the site of an occlusion in a blood vessel, it can be desirableto determine the physiologic effect of the occlusion on the patientbefore making a decision whether to implant the stent. One way todetermine the effect of the occlusion on the patient is to measure thedrop in blood pressure across the occlusion, such as using a FractionalFlow Reserve (FFR) technique. Generally speaking, if there is more thana 20% drop in pressure across the occlusion during maximum blood flow,the patient can be considered a candidate for stent implantation.Otherwise, it can be preferable to treat the patient with apharmaceutical regimen rather than implant a stent. Occlusions that lookvisibly similar, using an intravascular or other imaging modality, canbe vastly different in terms of pressure drop across the occlusion.Therefore, an accurate measurement of pressure drop across an occlusionmay help to tease out those occlusions that should be treated using astent from those occlusions that are adequately treated by apharmaceutical regimen.

As mentioned above, the present applicant has recognized, among otherthings, the advantages and desirability of miniaturization of an opticalfiber and optical fiber based pressure sensor for incorporation into acoronary guidewire, which, in turn, can optionally be used for guiding aballoon catheter or other device for positioning and securing the stentat the desired location. An optical fiber pressure sensor based on FBGtechnology can have an intrinsic pressure sensitivity of about 0.00038picometers (pm)/mmHg (about 0.02 pm/psi). Such an optical fiber pressuresensor based on FBG technology can have an intrinsic temperaturesensitivity of about 10 pm/degree Celsius (° C.). The temperaturesensitivity can increase if the optical fiber pressure sensor includesor is integrated or packaged with one or more materials having a highercoefficient of thermal expansion. The range of blood pressures in apatient is relatively low, e.g., about 0 millimeters of mercury (mmHg)to about 300 mmHg, and there is a need for high resolution within thatrange, e.g., 1-2 mmHg, where 51.7 mmHg equals 1 pound per square inch(psi), such as to adequately characterize the blood pressure drop acrossa blood vessel occlusion.

Based on these numbers, an uncompensated or uncorrected change intemperature of 0.1° C. can result in an equivalent intrinsic pressuredrift of about 2632 mmHg or more than 1000 times the desired bloodpressure measurement resolution. As mentioned above, when using anoptical fiber pressure sensor capable of insertion into a body lumen ofa patient, e.g., an animal such as a human, a small, uncompensated oruncorrected drift in temperature within the patient, e.g., as a resultof an injected imaging contrast medium, can appear as an artifact thatincorrectly indicates a large change in pressure. This can be due inpart to the relatively low intrinsic sensitivity of the optical fiberpressure sensor to pressure and the relatively high intrinsicsensitivity to temperature of the optical fiber associated with theoptical fiber pressure sensor. As such, a small, uncompensated drift intemperature can be unacceptable due to the need for accurate pressuremeasurements.

Using one or more techniques of this disclosure, a Fiber Bragg Grating(FBG) interferometer or other optical fiber pressure sensor guidewirecan be temperature compensated, such as for permitting accurate pressuresensing within a body lumen. In addition, this disclosure describestechniques for increasing the overall sensitivity of an optical fiberpressure sensor guidewire, such as to generate an easily detectableblood pressure indicating output signal providing the desired resolutionand accommodating the range of pressures associated with the patient.

It should be noted that the optical fiber described in this disclosurecan have a diameter of between about 25 microns and about 30 microns. Byway of comparison, a standard telecommunication optical fiber has adiameter of about 125 microns. This marked reduction in size can causenumerous challenges arising from the differences in the opticsproperties of such a drastically reduced size optical fiber.

FIG. 1 is a cross-sectional side view illustrating generally, by way ofexample, but not by way of limitation, an example of a strain-detectingor pressure-detecting optical FBG sensor 100 in an optical fiber 105.The FBG sensor 100 can sense pressure received from a nearby area, andcan transduce the received pressure into an optical signal within theoptical fiber 105. The FBG sensor 100 can include Fiber Bragg gratings110A-B in an optical fiber core 115, such as surrounded by an opticalfiber cladding 120. The gratings 110A-B can be separated by a strain orpressure sensing region 125, which, in an example, can be about amillimeter in length. In an example, strain or pressure can be sensed,such as by detecting a variation in length of the optical path betweenthese gratings 110A-B.

A Fiber Bragg Grating can be implemented as a periodic change in theoptical refractive index of a selected axial portion of the opticalfiber core 115. Light of specific wavelengths traveling down such aportion of the core 115 will be reflected. The period (distance orspacing) 130 of the periodic change in the optical index can determinethe particular wavelengths of light that will be reflected. The degreeof optical refractive index change and the axial length 135 of thegrating 110A-B can determine the ratio of light reflected to thattransmitted through the grating 110A-B.

FIG. 2 is a cross-sectional side view illustrating generally, by way ofexample, but not by way of limitation, an operative example of aninterferometric FBG sensor 100. The example of FIG. 2 can include twogratings 110A-B, which can act as mirrors that can both be partiallyreflective such as for a specific range of wavelengths of light passingthrough the fiber core 115. Generally, the reflectivity of each gratingof a particular pair of gratings 110A-B will be substantially similar tothe other grating in that particular pair of gratings 110A-B, but candiffer between gratings of a particular pair of gratings 110A-B forparticular implementations, or between different pairs of gratings110A-B, or both. This interferometric arrangement of FBGs 110A-B can becapable of discerning the “optical distance or optical pathlength”between FBGs 110A-B with extreme sensitivity. The “optical distance orpathlength” can be a function of the effective refractive index of thematerial of fiber core 115 as well as the physical distance 125 betweenFBGs 110A-B. Thus, a change in the refractive index can induce a changein optical path length, even though the physical distance 125 betweenFBGs 110A-B has not substantially changed.

An interferometer, such as can be provided by the FBG sensor 100, can beunderstood as a device that can measure the interference between lightreflected from each of the partially reflective FBGs 110A-B. When theoptical path length between the FBG gratings 110A-B is an exact integermultiple of the wavelength of the optical signal in the optical fibercore 115, then the light that passes through the FBG sensor 100 will bea maximum and the light reflected will be a minimum, such that theoptical signal can be substantially fully transmitted through the FBGsensor 100. This addition or subtraction of grating-reflected light,with light being transmitted through the optical fiber core 115, can beconceptualized as interference. The occurrence of full transmission orminimum reflection can be called a “null” and can occur at a precisewavelength of light for a given optical path length. Measuring thewavelength at which this null occurs can yield an indication of thelength of the optical path between the two partially reflective FBGs110A-B. In such a manner, an interferometer, such as can be provided bythe FBG optical fiber pressure sensor 100, can sense a small change indistance, such as a change in the optical distance 125 between FBGs110A-B resulting from a received change in pressure. In this manner, oneor more FBG sensors can be used to sense one or more pressures within abody lumen of a patient. This arrangement is an example of an FBGFabry-Perot interferometer, which can be more particularly described asan Etalon, because the physical distance 125 between the FBGs 110A-B issubstantially fixed.

The sensitivity of an interferometer, such as can be included in the FBGsensor 100, can depend in part on the steepness of the “skirt” of thenull in the frequency response. The steepness of the skirt can beincreased by increasing the reflectivity of the FBGs 110A-B, which alsoincreases the “finesse” of the interferometer. Finesse can refer to aratio of the spacing of the features of an interferometer to the widthof those features. To provide more sensitivity, the finesse can beincreased. The higher the finesse, the more resonant the cavity, e.g.,two FBGs and the spacing therebetween. The present applicant hasrecognized, among other things, that increasing the finesse or steepnessof the skirt of FBG sensor 100 can increase the sensitivity of the FBGsensor 100 to pressure within a particular wavelength range but candecrease the dynamic range of the FBG sensor 100. As such, keeping thewavelength of the optical sensing signal within the wavelength dynamicrange of the FBG sensor 100 can be advantageous, such as to provideincreased sensitivity to pressure. In an example, a closed-loop systemcan monitor a representative wavelength (e.g., the center wavelength ofthe skirt of the filtering FBG sensor 100). In response to suchinformation, the closed-loop system can adjust the wavelength of anoptical output laser to remain substantially close to the center of theskirt of the filter characteristic of the FBG sensor 100, even as forcesexternal to the optical fiber 105, such as bending and stress, can causeshifting of the center wavelength of the skirt of the filtercharacteristic of the FBG sensor 100.

In an example, such as illustrated in FIG. 2, the interferometric FBGsensor 100 can cause interference between that portion of the opticalbeam that is reflected off the first partially reflective FBG 110A withthat reflected from the second partially reflective FBG 110B. Thewavelength of light where an interferometric null will occur can be verysensitive to the “optical distance” between the two FBGs 110A-B. Theinterferometric FBG sensor 100 of FIG. 2 can provide another verypractical advantage. In the example illustrated in FIG. 2, the twooptical paths along the fiber core 115 are the same, except for thesensing region between FBGs 110A-B. This shared optical path can ensurethat any optical changes in the shared portion of optical fiber 105 willhave substantially no effect upon the interferometric signal; only thechange in the sensing region 125 between FBGs 110A-110B is sensed.Additional information regarding FBG strain sensors can be found in U.S.Patent Application Publication No. 2010/0087732 to Eberle et al., whichis incorporated herein by reference in its entirety, including itsdisclosure of FBGs and their applications.

FIG. 3 is a conceptual diagram illustrating various examples of FBGconfigurations of an FBG optical fiber pressure sensor 300, inaccordance with this disclosure. The FBG optical fiber pressure sensor300 can include an optical fiber 302 that can extend longitudinallythrough a stiff, rigid, or solid mounting 304. As seen in FIG. 3, aportion of the optical fiber 302 extends beyond a distal end 306 of themounting 304. The optical fiber 302 and the mounting 304 can be disposedwithin a housing 308. Using one or more techniques of this disclosure,such as shown and described in detail in this disclosure with respect toFIGS. 13-15, an optical fiber pressure sensor can include an opticalfiber that can be combined with a guidewire, such as for diagnosticassessment of a coronary obstruction, for example.

As described in more detail below, two or more FBGs, e.g., FBGs 1-4, canbe included in the FBG pressure sensor 300, such as for pressuresensing. One or more additional gratings can be included, and suchadditional one or more gratings can be insulated or isolated frominfluence caused by (1) bending (of the fiber) and/or (2) pressure.These insulated or isolated additional gratings can be arranged forproviding one or more of temperature calibration, compensation, orcorrection. In an example, the additional grating(s) can provide anindependent (of pressure and fiber bending) measure of temperature, suchas for feedback to a temperature compensation scheme or method of anoptical fiber pressure sensor 300. The optical fiber pressure sensor 300can optionally include a sealed or other cavity (not depicted in FIG.3), such as below a portion of the optical fiber 302, e.g., below FBG 3,which can amplify changes in pressure, or otherwise provide increasedoptical response to changes in pressure. Some example configurationsthat can include a sealed cavity are described in more detail below.

In FIG. 3, FBG 1 can be a FBG that produces a broad reflection band atthe center of the spectrum of FBG 1, such as shown generally at 400 inthe response diagram depicted in FIG. 4A, in which the x-axis representswavelength and the y-axis represents the intensity of the reflectedlight. FBG 2 and FBG 3, although depicted and referred to as separategratings, can represent a single FBG that can be split into twoidentical, smaller FBGs and separated by a small phase difference (orphase-shifted) of 180 degrees, for example.

For example, the phase shift could be built into a phase mask that isused to write the gratings onto the fiber, e.g., an electron beamgenerated phase mask. Illumination of the phase mask can result in aphase shift. In another example, a first grating can be written onto thefiber via a phase mask. Then, the phase mask can be moved by a distanceequivalent to a 180 degree phase shift, for example, and a secondgrating can be written onto the fiber.

The reflections from FBG 2 interfere with the reflections from FBG 3because of the phase shift between FBG 2 and FBG 3, shown as a phaseshift region 312A in FIG. 3. As a result, a narrow transmission notch402 is created within the reflection band shown generally at 404 in thewavelength response diagram depicted in FIG. 4A.

In an example, pressure changes can be detected by the optical fiberpressure sensor 300, e.g., within a patient's body, such as by detectingor amplifying the phase-shift between two FBGs, e.g., FBG 2 and FBG 3.This technique is in contrast to optical pressure sensing techniquesthat measure the shift in wavelength of the FBG itself. Using varioustechniques of this disclosure, the phase-shift between FBGs can bemodified rather than a wavelength shift of the FBG itself.

As seen in FIG. 3, FBG 3 can extend distally outward beyond the distalend 306 of the mounting 304. A change in pressure can cause the distalportion 310 of the optical fiber 302 to bend slightly against the distalend 306 of the mounting 304, which, in turn, can cause the distal end306 to mechanically act upon the phase-shift region 312A between FBG 2and FBG 3. The mechanical forces acting upon the phase-shift region 312Abetween FBG 2 and FBG 3 can concentrate a stress in the phase-shiftregion 312A of the optical fiber 302. The concentrated stress in thephase-shift region 312A changes the refractive index of the opticalfiber 302 in the stressed region, which, in turn, can alter, or amplify,the phase relationship between FBG 2 and FBG 3. The change inphase-shift between FBG 2 and FBG 3 can be quantified and the change inpressure can be determined from the quantified phase-shift.

For example, as described in more detail below, a wavelength of a narrowband laser (in relation to the wavelength response of FBGs 2 and 3) canbe locked on a point on a slope 406 of the narrow transmission notch 402in FIG. 4A, e.g., at about 50% of the depth of the notch 402. As thepressure changes, the notch 402 shifts and, consequently, the point onthe slope 406 shifts. A tracking circuit can then track the point on theslope 406, and a phase-shift can be determined from its change inposition. The intensity of reflected light will be modified when thenotch 402 moves. In the example in the diagram, if the notch 402 movesdownward in wavelength, then the intensity of the signal reflected willincrease. If the notch 402 moves upward in wavelength, then theintensity of the signal reflected will decrease. If it is chosen thatthe laser wavelength would be on the opposite side of the notch 402,then the effect would be reversed.

As indicated above, one or more external factors such as the temperaturecoefficient of one or more Fiber Bragg Gratings (FBGs) can besignificantly higher than the intrinsic pressure sensitivity of theoptical fiber pressure sensor that can include such FBGs. As such, asmall drift in temperature within a patient can spuriously appear as alarge change in pressure. Such a temperature-induced artifact in thepressure response signal may be unacceptable due to the need foraccurate pressure measurements. The present applicant has recognized,among other things, that it can be advantageous to provide the opticalfiber pressure sensor guidewire of this disclosure with a temperaturecompensated Fiber Bragg Grating (FBG) arrangement, such as foraccurately sensing pressure within a body lumen, for example.

The conceptual diagram of FIG. 3 can be used to describe severaldifferent configurations for a temperature compensated FBG optical fiberpressure sensor 300. Examples of more detailed configurations are shownand described below with respect to FIGS. 7-10 and FIG. 12.

In a first example of a configuration, a FBG optical fiber pressuresensor 300 can include FBGs 1-3 (FBG 4 need not be included). FBGs 2 and3, which can be configured to operate at the same wavelength (e.g., afirst wavelength between about 1000 nanometers (nm) and about 1700 nm),can form a phase-shift structure that can be used to sense pressure,such as described in detail above. To recap, a concentration in stressin the phase-shift region between the two gratings (e.g., FBG 2 and FBG3), as a result of the bending of the optical fiber 302 changes therefractive index of the optical fiber 302 in the phase-shift region. Thechange in the refractive index of the optical fiber 302 in thephase-shift region can alter the phase relationship between FBG 2 andFBG 3, which can be quantified, and the change in pressure can bedetermined from the quantified phase-shift. The phase-shift, however, isnot compensated for temperature, which may not acceptable, as explainedabove.

FBG 1 can be configured to be substantially independent of pressure,such as by locating it within the stiff, rigid, or solid mounting 308.Therefore, FBG 1 can be used to measure ambient temperature, such as toprovide a temperature compensated optical fiber pressure sensor. FBG 1can be configured to operate at a substantially different wavelengththan that of FBGs 2 and 3 (e.g., a second wavelength between 1000nanometers (nm) and 1700 nm). In this manner, FBG 1 has no interactionwith FBGs 2 and 3. As such, FBG 1 can provide a measure of ambienttemperature that is independent of pressure variations. In a mannersimilar to that described above with respect to tracking the change inposition of the notch 402 of FIG. 4A, a wavelength of a narrow bandlaser (in relation to the response of the FBG 1) can be locked on apoint on a slope 408 of the response of FBG 1 in FIG. 4A, e.g., at about50% of the depth of the response. The wavelength of the locked point onthe slope 408 shifts as the temperature changes. A tracking circuit canthen track the locked point on the slope 408 and a change in ambienttemperature can be determined from its change in position.

In order to generate a pressure signal that is ambient temperaturecompensated, the signal generated by FBG 1 can be used as a reference tonull a shift in temperature. A controller circuit can be configured tocontrol subtraction of the temperature reference signal (from FBG 1)from the temperature and pressure signal (from FBGs 2 and 3), such as togenerate a temperature compensated pressure signal. An example of atemperature compensation technique is described in more detail in thisdisclosure, such as with respect to FIG. 5.

In a second example of a configuration, the FBG sensor 300 can includean optical fiber, a stiff, rigid, or solid mounting, a housing, and FBGs1-3 (FBG 4 need not be included). FBGs 1-3 can be positioned very closeto each other and can thus form a very compact structure. FBGs 2 and 3,which can be configured to operate at the same wavelength (e.g., a firstwavelength between 1000 nm and 1700 nm), can form a phase-shiftstructure that can be used to sense pressure. The phase shift betweenFBGs 2 and 3 can result in a signal that changes with pressure andtemperature.

FBG 1 can be configured to operate at a similar, but slightly different,wavelength than that of FBGs 2 and 3 (e.g., a second wavelength near thefirst wavelength of FBGs 2 and 3 and between 1000 nm and 1700 nm). Inthis manner, FBG 1 can form a resonant feature with FBGs 2 and 3 at aslightly different wavelength. FBG 1 can result in a signal that changeswith respect to temperature changes.

A conceptual illustration of the response of FBGs 1-3 is depicted inFIG. 4B, where the x-axis represents wavelength and the y-axisrepresents the intensity of the reflected light. Again, the techniquesof this disclosure need not sense a shift in the wavelength of thegratings, but can instead sense a change in the phase between thegratings. The temperature compensating element, e.g., FBG 1, is inresonance with part of the pressure sensing structure, e.g., FBGs 2 and3. As such, FBG 1 can be linked to the pressure sensing structure ratherthan being an independent element. Such a configuration can provide acompact structure.

Similar to the first example of a configuration, such as to generate apressure signal that is temperature compensated, the signal generated byFBG 1 can be used as a reference, such as to null a shift intemperature. A slope 410 of the notch 412 and a slope 414 of the notch416 can each be tracked and used to determine changes in temperature andpressure, such as based on their respective changes in position. Acontroller circuit can be configured to control the subtraction of thetemperature reference signal (e.g., from FBG 1) from the temperature andpressure signal (e.g., from FBGs 2 and 3) such as to generate atemperature compensated pressure signal.

In a third example of a configuration, the FBG sensor 300 can include anoptical fiber, a stiff, rigid, or solid mounting, a housing, and FBGs1-4. FBGs 2 and 3, which can be configured to operate at the samewavelength, can form a first phase-shift structure that can be used tosense pressure. The phase shift between FBGs 2 and 3 can result in asignal that changes with pressure or temperature, or both.

FBGs 1 and 4, which can be configured to operate at the same wavelength,can form a second phase-shift structure that can be used to sensetemperature. The reflections from FBG 4 interfere with the reflectionsfrom FBG 1 because of the phase shift between FBG 4 and FBG 1, shown asa phase shift region 312B in FIG. 3. The phase shift between FBGs 1 and4 can result in a signal that changes with temperature and that isindependent of pressure.

A conceptual illustration of the response of FBGs 1-4 of the thirdexample of a configuration is depicted in FIG. 4C, where the x-axisrepresents wavelength and the y-axis represents the intensity of thereflected light. As seen in FIG. 4C, the response includes two notches418, 420. The third example of a configuration can provide more accuratemeasurements than the first example of a configuration because thenotches 418, 420 are generally more sensitive to any changes thanresponses without notches, e.g., the response 400 in FIG. 4A.

Similar to the first and second examples of configurations, in order togenerate a pressure signal that is temperature compensated, the signalgenerated by FBGs 1 and 4 can be used as a reference, such as to null ashift in temperature. A slope 422 of the notch 418 and a slope 424 ofthe notch 420 can each be tracked and used to determine changes intemperature and pressure based on their respective changes in position.A controller circuit can be configured to control subtraction of thetemperature reference signal (e.g., from FBG 1) from the temperature andpressure signal (e.g., from FBGs 2 and 3), such as to generate atemperature compensated pressure signal.

Using any one of the three examples of configurations described above,an optical fiber pressure sensor can be provided that can be suitablefor delivery within a body lumen, e.g., for diagnostic assessment ofcoronary obstructions. In addition, any one of the three examples ofconfigurations can compensate for temperature drift and can be fitted toa guidewire, such as for insertion into a body lumen of a patient. Inany of the three examples the wavelength of the FBGs used fortemperature calibration, compensation, or correction can be above orbelow the wavelength of the FBGs used for the pressure sensing.

Again, FIG. 3 is for conceptual purposes only and this disclosure is notlimited to the three example configurations described above with respectto FIG. 3. Other FBG configurations to sense pressure and compensate fortemperature drift are possible, examples of which are described in moredetail below.

In addition, as described in more detail below, various techniques aredisclosed for increasing the intrinsic sensitivity of an optical fiberpressure sensor, such as to generate an accurate output signal withinthe range of pressures associated with a patient. Generally speaking,these techniques can include focusing a response of a pressure sensormembrane into a smaller area, such as to increase the optical responseto the received pressure, e.g., from pressure waves.

FIGS. 4A-4C depict various wavelength response diagrams related to theconceptual diagram and examples of configurations described above withrespect to FIG. 3. In FIGS. 4A-4C, the x-axis represents wavelength andthe y-axis represents the intensity of the reflected light. The responsediagrams were described above in connection with the examples ofconfigurations of FIG. 3.

FIG. 5 is a block diagram of an example of an ambient temperaturecompensation technique that can be used to implement one or moretechniques of this disclosure. Although the example of a configurationof FIG. 5, shown generally at 500, will be particularly described withspecific reference to the third example of a configuration describedabove, it is applicable to each of the example configurations describedin this disclosure.

Initially, the optical fiber pressure sensor 300 of FIG. 3 can becalibrated, such as to ascertain the relative coefficients oftemperature and pressure for the sensor. The magnitudes of thesecoefficients can be stored in a memory device. A controller circuit canbe configured such that, during operation, it can read the coefficientsfrom the memory device and apply the pressure coefficient as a firstcoefficient X1 and the temperature coefficient as a second coefficientX2.

As described above, a first wavelength of a narrow band laser (inrelation to the response of FBGs 1 and 4) can be locked on a point onthe slope 422 of the narrow transmission notch 418 in FIG. 4C, e.g., atabout 50% of the length of the notch 418. A second wavelength of anarrow band laser (in relation to the response of FBGs 2 and 3) can belocked on a point on the slope 424 of the narrow transmission notch 420in FIG. 4C, e.g., at about 50% of the depth of the notch 420.

As the pressure changes, the notch 420 shifts and, consequently, thepoint on the slope 424 shifts. The tracking circuit can be configured tothen track the point on the slope 424. The magnitude of the change inwavelength, shown as λ1 in FIG. 5, can be input into a first multiplier502 and multiplied by the pressure coefficient X1. Similarly, as theambient temperature of the pressure sensor changes, the notch 418 shiftsand, consequently, the point on the slope 422 shifts. A tracking circuitcan then track the point on the slope 422. The magnitude of the changein wavelength, shown as λ2 in FIG. 5, can be input into a secondmultiplier 504 and multiplied by the ambient temperature coefficient X2.Similarly, The outputs of the multipliers 502, 504 can be input into afirst comparator 506, which can subtract any ambient temperature driftfrom the pressure measurement. In this manner, ambient temperaturenulling techniques can be used to provide accurate pressuremeasurements.

Also in accordance with this disclosure, a third wavelength that can beclose in magnitude to λ1 or λ2 but not in resonance with the phase shiftfeature can be used to monitor a total insertion loss of the system,e.g., from any bending, insertion of the optical fiber into a connector,etc. The insertion loss is generally a static number. During operation,the controller circuit can transmit the third wavelength λ3, which canbe input into a second comparator 508 along with the pressuremeasurement output from a first comparator 506, and the secondcomparator 508 can compensate the pressure measurement for any changesin insertion loss to produce a final pressure reading 510 for theoptical fiber pressure sensor.

Pressure sensors constructed using optical fibers can suffer fromsignificant pressure drift, due at least in part to the low intrinsicsensitivity of optical fibers (e.g., optical refractive index,mechanical size, etc.) to pressure. This is especially true for opticalfiber pressure sensors that are designed for low pressure applications,such as sensing the pressure within the human body.

As mentioned above, when using an optical fiber pressure sensor capableof insertion into a body lumen of a patient, e.g., an animal such as ahuman, a small, uncompensated or uncorrected drift in temperature withinthe patient, e.g., as a result of an injected imaging contrast medium,can appear as an artifact that incorrectly indicates a large change inpressure. This can be due in part to the relatively low intrinsicsensitivity of the optical fiber pressure sensor to pressure and therelatively high intrinsic sensitivity to temperature of the opticalfiber associated with the optical fiber pressure sensor. As such, asmall, uncompensated drift in temperature can be unacceptable due to theneed for accurate pressure measurements.

As described in more detail below with respect to FIGS. 6A-6B, one ormore techniques of this disclosure are described that can remove and/orcompensate for the effects of temperature drifts and other deleteriouseffects that might compromise the accuracy of the pressure reading. Forexample, polarization scrambling techniques, ambient temperature nullingtechniques, laser tracking techniques, and laser temperature monitoringtechniques can be used in combination to correct for temperature driftsthat can affect the accuracy of the pressure readings.

FIG. 6A is a block diagram of an example of a laser tracking system,shown generally at 600, in accordance with this disclosure. A controllercircuit 602 can be configured to control a laser 604 to generate andtransmit the light from a narrow band laser into a first port (e.g.,port 1) of a circulator 606. The circulator 606 can route the light outa second port (e.g., port 2) toward the optical fiber pressure sensor.The controller circuit 602 can be configured to set the wavelength ofthe laser on a point on a slope of a notch in the wavelength response ofan FBG, such as described above. Any light reflected back from theoptical fiber pressure sensor can enter the second port (e.g., port 2)of the circulator 606 and can be routed out a third port (e.g., port 3)and received by an optical detector 608.

As indicated above, laser tracking techniques can be used to correct fortemperature drift. In accordance with this disclosure, the laser 604 canbe actively locked at a position on a slope of a transmission notch,e.g., slope 406 of the notch 402 of FIG. 4A. Then, the system 600 canmeasure the change in wavelength and, in response, alter the laser'soperating characteristics, e.g., drive current.

In the system 600 of FIG. 6A, a first comparator 610 can be used toprovide laser tracking. The optical power of the reflected signal, whichis output by the optical detector 608, can be a first input to a firstcomparator 610. A locking set point value 612 can be a second input tothe first comparator 610. The first comparator 610 can compare the twoinputs and then output a value that can be applied as an input to alaser drive current control 614 that can modulate the drive current ofthe laser 604. In this manner, the configuration of FIG. 6A can providea locking loop to maintain a set point on the slope of a notch, forexample.

In one example implementation, during initial setup a user can adjustthe conditions of the laser 604 so that the wavelength of the laser 604is slightly greater than the wavelength of the transmission notch. Theuser can adjust the wavelength of the laser 604 by adjusting the drivecurrent of a thermoelectric cooler (TEC) of the laser 604 (large shiftsin wavelength), which can alter the temperature of a submount of thelaser 604, or adjust the drive current of the laser 604 itself (smallshifts in wavelength).

Once the initial setup of the laser 604 is complete, the user caninitiate the tracking techniques of this disclosure. The trackingtechniques begin to reduce the drive current to the laser 604, which, inturn, decrease the wavelength of the laser. More particularly, as thewavelength of the laser 604 decreases toward the wavelength of thetransmission notch, the comparator 610 compares the signal from theoptical detector 608 and the locking set point value 612. If the signalfrom the optical detector 608 is higher than the locking set point value612, the drive current of the laser 604 can be reduced via feedback fromthe comparator 610 to the laser drive current control 614. In someexamples, reducing the laser drive current by 0.25 milliamps (mA) canshift the wavelength by 1 pm, where the coefficient of the laser 604 isabout 4 pm per 1 mA of drive current.

During operation, the wavelength of the locked point on the slope canshift as the ambient temperature changes. If the wavelength of thetransmission notch increases or decreases, the system 600 increases ordecreases, respectively, the drive current of the laser 604 in order totrack the transmission notch. As indicated above, the laser 604 can, forexample, be locked on a point on a slope of the narrow transmissionnotch at about 50% of the depth of the notch 402. These trackingtechniques can track the position of the locked point on the slope and achange in temperature can be determined from the change in position. Thedetermined change in temperature can be an input into an algorithmexecuted by a pressure reading module 622, which can use the determinedchange in temperature to calculate an accurate pressure reading. Thepressure reading module 622 can be, for example, machine orcomputer-implemented at least in part. For example, the controller 602can execute instructions encoded on a computer-readable medium ormachine-readable medium that implement the techniques and algorithmsascribed to the pressure reading module 622.

One advantage of tracking the shift in wavelength of the FBG sensor bymodulating the drive current of the laser is that it can linearize theresponse of the circuit and can be more forgiving of different powerlevels. That is, regardless of the insertion loss of the pressuresensor, which can vary by construction variables or variations inconnecting in-line optical connectors, the amount by which the drivecurrent will change for a given wavelength shift will be constant.Optical fiber pressure sensors that utilize a change in power todemodulate the signal are sensitive to changes in built in or fixedinsertion loss. By knowing the shift in laser wavelength for a givendrive current change, the current reading can be converted to awavelength and hence to a pressure reading.

Optical sensing schemes exist that directly measure the change inwavelength of the sensor response. In one example, the sensor can beilluminated with broadband light and the spectral response can bemeasured with an Optical Spectrum Analyzer (OSA). This is not feasiblefor this application as the update times can be too slow and therequired wavelength precision is beyond this type of instrument.Alternatively, techniques exist that measure the change in intensity ofthe optical power as the laser tracks up and down the slope of the FBGsensor. One disadvantage of this technique, however, is that the powerresponse will be non-linear for large excursions as the laser approachesthe top of the filter (lower slope) and the bottom of the filter (higherslope). Without compensation this technique can yield inaccurateresults.

Continuing with the description of FIG. 6A, the output of the firstcomparator 610 can be applied as a first input to a second comparator616. A zero pressure DC value 618 can be applied as a second input tothe second comparator 616, which can subtract the initial DC value andoutput a zero pressure reading. The outputted zero pressure reading fromthe second comparator 616 can be multiplied at a multiplier 620 by acoefficient of wavelength shift with the drive current that results inan output of an actual wavelength shift. The outputted actual wavelengthshift can then be converted to a pressure reading at 622.

As indicated above, laser temperature monitoring techniques can be usedto correct for temperature drifts that can affect the accuracy of thepressure readings. The lasers used to implement the various techniquesdescribed in this application have a wavelength dependency on thetemperature at which they operate. A typical laser will have awavelength dependency on operating temperature of 100 pm per degreeCelsius (° C.). A well controlled laser may have temperature stabilityof 0.01° C. giving a wavelength drift of 1 pm. As indicated above,however, a shift of 1 pm is equivalent to a very large pressuredifference and, as such, should be accounted for in the final pressurereading.

Rather than stabilize the laser temperature to the degree required,which can increase the complexity and expense of the system 600, thisdisclosure describes techniques that can accurately monitor thetemperature through a thermistor that is built-in to the submount of thelaser 604 and that can apply this temperature information to acorrection algorithm for the final pressure reading 622. To accuratelymonitor the temperature through the thermistor, the system 600 of FIG.6A can include an electronic circuit 624, e.g., outside the opticalsystem, that is configured to measure the voltage across the thermistorof the submount of the laser 604. The electronic circuit 624 can includean amplifier that can amplify the voltage signal with high enough gainthat to resolve temperature changes on the order of 1/1000^(th) of adegree Celsius. These changes are on the order of hundreds of microvolts(μV). As such, it can be desirable to use high quality circuits composedof instrumentation amplifiers, for example.

In one example implementation, rather than amplifying the voltage acrossthe thermistor, the electronic circuit 624 can subtract an offsetvoltage from the voltage across the thermistor, e.g., the operatingvoltage of the laser, before amplification. Then, the electronic circuit624 can amplify the resulting voltage value, which is close to zero. Inthis manner, the electronic circuit 624 allows small changes in thetemperature of the laser to be determined. The temperature change can beconverted to wavelength and then to the equivalent pressure, which canthen be used to determine the true pressure reading at 622.

The output from the laser, e.g., laser 604, can have a strong degree oflinear polarization at the exit from the laser package. It istechnically possible to preserve this linear polarization by usingpolarization maintaining fiber and components along the entire opticalpath to the FBGs. If the polarization is preserved such that the lightincident upon the FBGs is aligned preferentially with a particularbirefringent axis, then the response of the light to the FBGs would notbe affected by the birefringence. Unfortunately, preserving thepolarization in this manner is both complex and expensive.

In the absence of polarization maintaining measures, the light from thelaser can arrive at the FBGs with any state of polarization depending onthe nature of the optical path through which the light has travelled.Significant bending or twisting of the fiber and the birefringent natureof any components through which the light has travelled can alter thestate of polarization (SOP). Although the SOP that arrives at the FBGsis not controlled, it nevertheless can have a high degree ofpolarization (DOP) as this characteristic is very difficult to fullyrandomize. A high DOP means the exact interaction of the light and thebirefringent axes of the FBGs can change if there are perturbations tothe system, such as bending of the guidewire during a procedure. Forthis reason, the system 600 of FIG. 6A can utilize polarizationscrambling techniques to overcome the effects of birefringence anddetermine a true pressure reading. The polarization scramblingtechniques scramble or average a range of polarization states so thefinal result is not biased to any given combination of birefringent axisof the FBG and incident polarization state.

Optical fiber pressure sensors such as the FBGs of this disclosure aresubject to the effects of birefringence in the optical fiber, due to thephysical imperfections of the fiber. With birefringence, differentpolarizations of light can have slightly different effective opticalrefractive indices. An effective index of the fiber that is differentfor different polarizations can result in a slightly different Braggwavelength. A different Bragg wavelength can result in the appearance ofmovement of the point on the slope of the transmission notch at whichthe laser is locked. In reality, however, the point may not have movedat all.

A typical optical fiber can have birefringence on the order of 2.5×10⁻⁶,which translates to a wavelength shift between the most differentpolarizations of 4 pm. A 4 pm wavelength shift would be equivalent to arelatively massive pressure change and, as such, should be accounted forin the final pressure reading.

The exact wavelength of the FBG can be determined by a combination ofthe refractive index of the medium and the physical spacing of theplanes or fringes that make up the FBG, as in the following equation:1_(B)=2n _(e) L, where 1_(B)=Bragg wavelength,n _(e)=effectiverefractive index, and L=spacing of fringes.

The polarization scrambling techniques of this disclosure can beimplemented by sweeping a series of “optical waveplates” through apseudo-random pattern with sufficient frequency that the desired signalwill be averaged satisfactorily. Optical waveplates are devices that canalter the state of polarization. In order to measure a typicalcardiovascular pressure profile with a heart rate of 0 beats per minuteto 200 beats per minute, scrambling techniques can average at a ratethat is sufficient to capture the dynamic profile, e.g., an effectivefrequency of several hundred hertz.

In the system 600 of FIG. 6A, the optical waveplates can be physicallylocated between where the laser beam exits laser 604 and the FBGs of theoptical fiber pressure sensor. In one example, an optical waveplate canbe formed by wrapping a portion of the optical fiber around apiezoelectric material and by stretching the fiber upon application of avoltage to the piezoelectrical material. In another example, an opticalwaveguide can be used to form an optical waveplate. The application of avoltage across electrodes built into the optical waveguide can result inthe change of the refractive index.

Using the polarization scrambling techniques of this disclosure, it isnot necessary to know the levels or patterns of birefringence in thesystem because the polarization controlling techniques do not rely uponfeedback. Instead, the polarization scrambling techniques rely on anaveraged polarization that is achieved by sweeping through as manyavailable polarization states to get an average polarization value sothe final result is not biased to any given combination of birefringentaxis of the FBG and incident polarization state. Additional informationregarding how the polarization scrambling techniques are used todetermine a true pressure reading are disclosed in U.S. ProvisionalApplication No. 61/709,700, titled “POLARIZATION SCRAMBLING FORINTRA-BODY FIBER OPTIC SENSOR”, by Howard Rourke, et al. and filed onOct. 4, 2012, the entire content of which being incorporated herein byreference.

FIG. 6B is a block diagram of an example of a temperature compensationtechnique in accordance with this disclosure. As described above, inorder to determine an accurate pressure reading, both the ambienttemperature of the optical fiber pressure sensor and the temperaturedrift of the laser should be accounted for in the final pressure readingat 622 of FIG. 6A. In FIG. 6B, a first laser 630 can be locked onto aphase-shift region, e.g., phase-shift region 312A between FBG 2 and FBG3 of FIG. 3. This phase-shift region, however, is not compensated forthe ambient temperature of the pressure sensor and, as such, reacts toboth pressure and temperature. Using either a measurement of the changein drive current of the laser, e.g., in milliamps, or a measurement ofthe change in wavelength, the controller 602 of FIG. 6A can determinethe shift in wavelength at 632. Further, using the techniques describedabove, the controller 602 can determine the operating temperature of thefirst laser 630 at 634 by measuring the voltage across the submountthermistor via the electronic circuit 624 of FIG. 6A. The controller 602can correct the determined shift in wavelength for the operatingtemperature of the first laser 630 by subtracting the determinedoperating temperature of the first laser 630 from the shift inwavelength determined at 636. Next, the corrected wavelength shift canbe scaled to an equivalent pressure at 638, e.g., converted from avoltage value to a pressure value. The corrected wavelength shift at 636and its scaled value at 638, however, have not been corrected for theambient temperature of the pressure sensor.

In order to correct for the ambient temperature of the pressure sensor,a second laser 640 can be locked onto another phase-shift region, e.g.,phase-shift region 312B between FBG 1 and FBG 4 of FIG. 3. Thisphase-shift region is insensitive to pressure and responds only to theambient temperature of the pressure sensor. Using either a measurementof the change in drive current of the laser, e.g., in milliamps, or achange in wavelength, the controller 602 of FIG. 6A can determine theshift in wavelength at 642. The controller 602 can also determine thetemperature of the second laser 640 at 644 by measuring the voltageacross the submount thermistor via the electronic circuit 624 of FIG.6A. The controller 602 can correct the determined shift in wavelengthfor the operating temperature of the second laser 640 by subtracting thedetermined operating temperature of the second laser 640 from the shiftin wavelength determined at 646. Next, the corrected wavelength shiftcan be scaled to an equivalent pressure at 648, e.g., converted from avoltage value to a pressure value. Finally, at 650, the pressuredetermined at 648 can be subtracted from the pressure determined at 638in order to determine a true pressure reading.

FIGS. 7A-7C depict an example of a pressure sensor that can be used toimplement one or more techniques of this disclosure. The example of thepressure sensor depicted in FIGS. 7A-7C is an example of a standalonepressure sensor that can use one or more phase shift gratings. The typeof grating written into the fiber can be, for example, a “phase shift”grating or a “Fabry Perot” grating. A “standalone” sensor can be capableof sensing pressure independently of the fiber being attached to a guidewire core subassembly. In contrast, an “integrated” pressure sensor caninvolve placing the fiber with the appropriate gratings written in it ona guide wire core and then completing the sensor once the fiber ispositioned on the wire.

FIG. 7A is an example of a perspective view of an example of a opticalfiber pressure sensor 700 that can include an optical fiber 702, whichcan be configured to transmit one or more optical sensing signals, and atemperature compensated Fiber Bragg Grating (FBG) interferometer (showngenerally at 704 in FIG. 7C) that can be included in, or in opticalcommunication with, the optical fiber 702. The FBG interferometer 704can be configured to receive pressure (e.g., from pressure waves), andto modulate, in response to the received pressure, an optical sensingsignal being delivered via the optical fiber 702 to the FBGinterferometer 704. The pressure sensor 700 can include a sensormembrane 706, which can be in physical communication with the FBGinterferometer 704. The sensor membrane 706 can be configured to helptransmit the pressure to the FBG interferometer 704. The pressure sensor700 can further include a sheath 708 that can, for example, help containcomponents of the pressure sensor 700 and/or help ease the pressuresensor through the vascular system.

FIG. 7B is an example of a cross-sectional end view of the pressuresensor 700 of FIG. 7A. As seen in FIG. 7B, the optical fiber 702 canextend through the pressure sensor 700, such as at substantially anaxial center of the pressure sensor 700.

FIG. 7C is an example of a cross-sectional side view of the pressuresensor 700 of FIG. 7A, such as can be taken along section A-A of FIG.7B. FIG. 7C depicts the optical fiber 702 extending through a proximalportion 710 and a distal portion 712 of the pressure sensor 700. Aproximal portion of the phase shift grating of FBG interferometer 704can be captured by a stiff, rigid, or solid supporting member 714, e.g.,via bonding. The supporting member 714 can be a capillary tube, forexample.

In the distal portion 712, the pressure sensor 700 can define a cavity716, e.g., filled with air, such as laterally below the distal portionof the phase shift grating of FBG interferometer 704 and laterally belowthe remaining distal length of the fiber 702 extending distally axiallybeyond the phase shift grating. In the example shown in FIG. 7C, theflexible sensor membrane 706 can be thick enough such that it contactsthe fiber 702 and the fiber 702 can be attached to the flexible sensormembrane 706, e.g., via bonding. The flexible sensor membrane 706 caninclude, for example, a thin polymer film, a heat seal film, or a thinmetal foil. The flexible sensor membrane 706 can be attached to thepressure sensor 700, such as via bonding or solder. In an example, themembrane 706 can be made by casting a silicone layer.

The pressure sensor 700 can be sealed on both the proximal end 718 andthe distal end 720. In addition, the sensor membrane 706 can be sealedcreating the sealed cavity 706.

The example pressure sensor 700 of FIG. 7C depicts three FBGs, namelyFBGs 1-3, along with an optional FBG, namely FBG 4. FBG 1 is independentof pressure and can be used for temperature measurements to provide atemperature compensated optical fiber pressure sensor, as describedabove with respect to FIG. 3 and FIG. 4A.

FBGs 2 and 3 can form a phase-shift FBG structure. The surface area ofthe membrane 706 can concentrate a change in pressure and can focus amechanical response to the change in pressure at the phase-shift regionbetween FBG 2 and FBG 3. This can enhance the sensitivity of thepressure sensor 700. The mechanical forces acting upon the phase-shiftregion between FBG 2 and FBG 3 can concentrate a stress in thephase-shift region. The concentrated stress in the phase-shift regioncan change the refractive index of the optical fiber 702, which, inturn, alters the phase relationship between FBG 2 and FBG 3. The changein phase-shift between FBG 2 and FBG 3 can be detected and quantified,and the change in pressure can be determined from the quantifiedphase-shift.

In an example, the pressure sensor 700 can optionally further includeFBG 4, e.g., located axially more proximal than FBG 1. As describedabove with respect to FIG. 3 and FIG. 4C, FBGs 1 and 4 can form aphase-shifted FBG structure that can be used to detect and quantify achange in temperature in the pressure sensor 700, which can besubstantially independent of any pressure variations, due to thelocation of FBGs 1 and 4 within the stiff, rigid, or solid supportingmember 714. In the configuration shown in FIG. 7C, the supporting member714 can be disposed about FBGs 1, 2, and 4.

FIGS. 8A-8C depict another example of a pressure sensor that can be usedto implement one or more techniques of this disclosure, such as can usea standalone pressure sensor that can use one or more phase shiftgratings.

FIG. 8A is a perspective view of an example of an optical fiber pressuresensor 800 that can include an optical fiber 802, which can beconfigured to transmit one or more optical sensing signals, and atemperature compensated Fiber Bragg Grating (FBG) interferometer (showngenerally at 804 in FIG. 8C) in optical communication with the opticalfiber 802. The FBG interferometer 804 can be configured to receivepressure (e.g., from pressure waves), and to modulate, in response tothe received pressure, the optical sensing signal. The pressure sensor800 can include a sensor membrane 806 that can be in physicalcommunication with the FBG interferometer 804. The sensor membrane 806can be configured to transmit the pressure to the FBG interferometer804. The pressure sensor 800 can further include a sheath 808 that can,for example, help contain components of the pressure sensor 800 and/orhelp ease the pressure sensor through the vascular system.

FIG. 8B is an example of a cross-sectional end view of the pressuresensor 800 of FIG. 8A. As seen in FIG. 8B, the optical fiber 802 canextend through the pressure sensor 800, such as at substantially anaxial center of the pressure sensor 800.

FIG. 8C is an example of a cross-sectional side view of the pressuresensor 800 of FIG. 8A, such as can be taken along section A-A of FIG.8B. The optical fiber 802 can be supported in part by a stiff, rigid, orsolid supporting member 814. The pressure sensor 800 can define a cavity816, e.g., filled with air.

As seen in FIG. 8C, the sensor membrane 806 can include a taperedportion 818 that can extend inwardly toward an axial center of thepressure sensor 804. The tapered portion 818 can help focus the responseof the membrane 806 against the phase-shift region between FBG 2 and FBG3, thereby further concentrating a stress in the phase-shift region,which can enhance the sensitivity of the pressure sensor 800.

In an example, a portion of the supporting member 814 can define areservoir 820 that can be adjacent to the fiber 802. The reservoir 820can be filled with a gas, e.g., air. In one example, the reservoir canbe filled with a gas, e.g., nitrogen, that can provide greatertemperature stability than air. In one example, the reservoir 820 can bea vacuum that can provide temperature stability. The reservoir 820 canprovide a configuration that can be adjacent a limited cavity 816immediately laterally below the fiber 802 between FBG 2 and FBG 3 suchthat it can be acted upon by the portion 818 yet the reservoir 820 stillincludes a large compressible volume.

In an example, such as shown in FIG. 8C, the flexible sensor membrane806 can include, for example, a thin polymer film, a heat seal film, ora thin metal foil. The flexible sensor membrane 806 can be attached tothe pressure sensor 800, such as via bonding or solder. In an example,the membrane 806 can be made by casting a silicone layer.

The pressure sensor 800 can be sealed on both the proximal end 817 andthe distal end 819. The sensor membrane 806 can be sealed, such as forcreating the sealed cavity 816.

The example of a pressure sensor 800 of FIG. 8C can include three FBGs(e.g., FBGs 1-3) along with an optional FBG (e.g., FBG 4). FBG 1 can beconfigured to be independent of pressure and can be used for temperaturemeasurement, such as to provide a temperature compensated optical fiberpressure sensor, such as described above with respect to FIG. 3 and FIG.4A.

FBGs 2 and 3 can form a phase-shifted FBG structure. The surface area ofthe membrane 806 can be configured to concentrate a change in pressureonto the portion 818, which can focus a mechanical response to thepressure at the phase-shift region between FBG 2 and FBG 3. Themechanical force acting upon the phase-shift region between FBG 2 andFBG 3 can concentrate a stress in the phase-shift region. Theconcentrated stress in the phase-shift region can change the refractiveindex of the optical fiber 802, such as to alter the phase relationshipbetween FBG 2 and FBG 3. The change in phase-shift between FBG 2 and FBG3 can be detected and quantified, and the change in pressure can bedetermined from the quantified phase-shift.

The pressure sensor 800 can optionally further include FBG 4, e.g.,located axially more proximal than FBG 1. As described above withrespect to FIG. 3 and FIG. 4C, FBGs 1 and 4 can form a phase-shifted FBGstructure that can be used to detect and quantify a change intemperature in the pressure sensor 800. In the configuration shown inFIG. 8C, the supporting member 814 is not disposed about FBGs 1, 2, and4, in contrast to the configuration example of FIG. 7C.

FIGS. 9A-9C depict another example of a pressure sensor that can be usedto implement one or more techniques of this disclosure. The example ofthe pressure sensor depicted in FIGS. 9A-9C can provide a standalonepressure sensor that can use one or more phase shift gratings.

FIG. 9A is a perspective view of an optical fiber pressure sensor 900that can include an optical fiber 902, which can be configured totransmit one or more optical sensing signals, and a temperaturecompensated Fiber Bragg Grating (FBG) interferometer (shown generally at904 in FIG. 9C), such as in optical communication with the optical fiber902. The FBG interferometer 904 can be configured to receive pressure(e.g., from pressure waves), and to modulate, in response to thereceived pressure, the optical sensing signal. The pressure sensor 900can include a sensor membrane 906 that can be in physical communicationwith the FBG interferometer 904. The sensor membrane 906 can beconfigured to transmit the pressure to the FBG interferometer 904. Thepressure sensor 900 can further include a sheath 908 that can, forexample, help contain components of the pressure sensor 900 and/or helpease the pressure sensor through the vascular system.

FIG. 9B is an example of a cross-sectional end view of the pressuresensor 900 of FIG. 9A. As seen in FIG. 9B, the optical fiber 902 canextend through the pressure sensor 900 at a position that is offset froman axial center of the pressure sensor 900.

FIG. 9C is an example of a cross-sectional side view of the pressuresensor 900 of FIG. 9A, such as can be taken along section A-A of FIG.9B. FIG. 9C depicts the optical fiber 902 extending through a proximalportion 910 and a distal portion 912 of the pressure sensor 904. Aproximal portion of the FBG interferometer 904 can be captured by asupporting member 914, e.g., via bonding. The supporting member 914 caninclude a capillary tube, for example. In the distal portion 912, thepressure sensor 900 can define a cavity 916, e.g., filled with air.

As seen in the example shown in FIG. 9C, the sensor membrane 906 can bein mechanical communication with a portion 921 that can extend laterallyinwardly into the pressure sensor 904. The portion 921 can focus theresponse of the membrane 906 against the phase-shift region between FBG2 and FBG 3, which can thereby further concentrate a stress in thephase-shift region, which can enhance the sensitivity of the pressuresensor 900.

In the example shown in FIG. 9C, the flexible sensor membrane 906 caninclude, for example, a thin polymer film, a heat seal film, or a thinmetal foil. The flexible sensor membrane 806 can be attached to thepressure sensor 900, such as via bonding or solder. In an example, themembrane 906 can be made by casting a silicone layer.

The pressure sensor 900 can be sealed on both the proximal end 918 andthe distal end 920. In addition, the sensor membrane 906 can be sealedcreating the sealed cavity 916.

The example of a pressure sensor 900 of FIG. 9C can include three FBGs(e.g., FBGs 1-3), along with an optional FBG (e.g., FBG 4). FBG 1 can beconfigured to be independent of pressure, such as explained above, andcan be used for temperature measurement, such as to provide atemperature compensated optical fiber pressure sensor, such as describedabove with respect to FIG. 3 and FIG. 4A.

FBGs 2 and 3 can form a phase-shifted FBG structure. The surface area ofthe membrane 906 can concentrate any change in pressure into the portion921, which can focus a mechanical response to the pressure at thephase-shift region between FBG 2 and FBG 3. The mechanical forces actingupon the phase-shift region between FBG 2 and FBG 3 can concentrate astress in the phase-shift region. The concentrated stress in thephase-shift region can change the refractive index of the optical fiber902, such as to alter the phase relationship between FBG 2 and FBG 3.The change in phase-shift between FBG 2 and FBG 3 can be detected andquantified, and the change in pressure can be determined from thequantified phase-shift. The pressure sensor 900 can include a compliantlayer 919 laterally underneath the optical fiber 902, such as to allowthe portion 921 to act on the optical fiber 902 without damaging theoptical fiber 902.

The pressure sensor 900 can optionally further include FBG 4, e.g.,located more proximal than FBG 1. As described above with respect toFIG. 3 and FIG. 4C, FBGs 1 and 4 can form a phase-shifted FBG structurethat can be used to quantify a change in temperature in the pressuresensor 800. In the configuration shown in FIG. 9C, the supporting member914 can be disposed about FBGs 1 and 4.

FIGS. 10A-10D depict an example of a pressure sensor that can be used toimplement one or more techniques of this disclosure. The example of apressure sensor depicted in FIGS. 10A-10D can provide an examplestandalone pressure sensor that can use one or more “Fabry Perot”grating arrangements.

FIG. 10A is an example of a perspective view of an optical fiberpressure sensor 1000 that can include an optical fiber 1002, which canbe configured to transmit one or more optical sensing signals, and atemperature compensated Fiber Bragg Grating (FBG) interferometer (showngenerally at 1004 in FIG. 10D) that can be in optical communication withthe optical fiber 1002. The FBG interferometer 1004 can be configured toreceive pressure (e.g., from pressure waves), and to modulate, inresponse to the received pressure, the optical sensing signal. Thepressure sensor 1000 can include a sensor membrane 1006 that can be inphysical communication with the FBG interferometer 1004. The sensormembrane 1006 can be configured to transmit the pressure to the FBGinterferometer 1004. The pressure sensor 1000 can further include asheath 1008 that can, for example, help contain components of thepressure sensor 1000 and/or help ease the pressure sensor through thevascular system.

FIG. 10B is an example of a cross-sectional end view of the pressuresensor 1000 of FIG. 10A, depicting an example of a location of theoptical fiber 1002. As seen in the example of FIG. 10B, the opticalfiber 1002 can extend axially through the pressure sensor 1000, such asat a position that is axially offset from an axial center of thepressure sensor 1000. FIG. 10C is an example of a cross-sectional endview of the pressure sensor without the optical fiber 1002.

FIG. 10D is an example of a cross-sectional side view of the pressuresensor 1000 of FIG. 10A, such as can be taken along section A-A of FIG.10C. FIG. 10D depicts an example of the optical fiber 1002 extendingthrough a proximal portion 1010 and a distal portion 1012 of thepressure sensor 1004. A proximal portion of the optical fiber 1002 canbe captured by a first supporting member 1014A and a distal portion 1012of the optical fiber 1002 can be captured by a second supporting member1014B, e.g., via bonding.

The pressure sensor 1000 can include a sensor member 1006. The pressuresensor 1000 can define a cavity 1016, e.g., filled with air, laterallybelow the sensor membrane 1006. The sensor membrane 1006 and the cavity1016 can concentrate a stress in the area between the Fabry-Perotgratings FBG 1 and FBG 2, which can enhance the sensitivity of thepressure sensor 1000.

The flexible sensor membrane 1006 can include, for example, a thinpolymer film, a heat seal film, or a thin metal foil. The flexiblesensor membrane 1006 can be attached to the pressure sensor 1000, suchas via bonding or solder. In an example, the membrane 1006 can be madeby casting a silicone layer.

The pressure sensor 1000 can be sealed on both the proximal end 1018 andthe distal end 1020. The sensor membrane 1006 can be sealed, such as forcreating the sealed cavity 1016.

The example of a pressure sensor 1000 of FIG. 10D can include four FBGs(e.g., FBGs 1-4). FBGs 3 and 4 can form a phase-shifted FBG structure,such as for sensing temperature. The change in phase-shift between FBG 3and FBG 4 can be detected and quantified, and the change in temperaturecan be determined from the quantified phase-shift, such as describedabove.

The pressure sensor 1000 can further include Fabry-Perot gratings FBG 1and FBG 2, which can be used to sense changes in pressure. Similar tothe phase-shift grating structures described above with respect to FIGS.7-9, the Fabry-Perot gratings FBG 1 and FBG 2 can create a phase shiftthat can be tracked in a manner similar to that described above. Thatis, a notch can be created in the wavelength response to the Fabry-Perotgratings FBG 1 and FBG 2, as shown and described in more detail withrespect to FIG. 11. A point on a slope of the notch can be set andtracked, a phase shift can be detected and quantified, and the change inpressure can be determined from the quantified phase-shift, such asdescribed in detail above.

FIG. 11 depicts an example of a conceptual response diagram related tothe example of a pressure sensor shown in FIG. 10D. In particular, FIG.11 depicts a conceptual wavelength response of the Fabry-Perot gratingsFBG 1 and FBG 2 of FIG. 10D. As seen in the example shown in FIG. 11,the wavelength response of the Fabry-Perot gratings FBG 1 and FBG 2 caninclude three notches, 1100, 1102, 1104. This is in contrast to thewavelength responses of the phase-shift structures shown in FIGS. 4A-4C,which can include a single notch for a pair of FBGs. The additionalnotches in FIG. 11 can be a result of the increased distance between theFabry-Perot gratings FBG 1 and FBG 2. As the distance between theFabry-Perot gratings FBG 1 and FBG 2 increases, additional notches canoccur. As the distance between the Fabry-Perot gratings FBG 1 and FBG 2decreases, notches can disappear until the response resembles that ofthe phase-shift structures described above.

In a manner similar to that described above, a wavelength of a narrowband laser (in relation to the response of FBGs 1 and 2) can be lockedon a point on a slope 1106 of a narrow transmission notch, e.g., notch1102, in FIG. 11, e.g., at about 50% of the length of the notch 1102. Asthe pressure changes, the notch 1102 and, consequently, the point on theslope 1106 shifts. A tracking circuit can then track the point on theslope 1106 and a phase-shift can be determined from its change inposition. The intensity of reflected light will be modified when thenotch 1106 moves. A phase shift can be quantified, and the change inpressure can be determined from the quantified phase-shift, such asdescribed in detail above.

FIGS. 12A-12C depict another example of a pressure sensor that can beused to implement one or more techniques of this disclosure. The exampleof a pressure sensor depicted in FIGS. 12A-12C can provide anotherexample standalone pressure sensor that can use one or more Fabry-Perotgrating arrangements.

FIG. 12A is an example of a perspective view of an optical fiberpressure sensor 1200 that can include an optical fiber 1202 that can beconfigured to transmit one or more optical sensing signals and atemperature compensated Fiber Bragg Grating (FBG) interferometer (showngenerally at 1204 in FIG. 12C) in optical communication with the opticalfiber 1202. The FBG interferometer 1204 can be configured to receivepressure, e.g., from pressure waves, and to modulate, in response to thereceived pressure, the optical sensing signal. The pressure sensor 1200can include a sensor membrane 1206 that can be in physical communicationwith the FBG interferometer 1204. The sensor membrane 1206 can beconfigured to transmit the pressure to the FBG interferometer 1204. Thepressure sensor 1200 can further include a sheath 1208 that can, forexample, help contain components of the pressure sensor 1200 and/or helpease the pressure sensor through the vascular system.

FIG. 12B is an example of a cross-sectional end view of the pressuresensor 1200 of FIG. 12A. As seen in FIG. 12B, the optical fiber 1202 canextend axially through the pressure sensor 1200 such as at substantiallyan axial center of the pressure sensor 1200.

FIG. 12C is an example of a cross-sectional side view of the pressuresensor 1200 of FIG. 12A, such as can be taken along section A-A of FIG.12B. The optical fiber 1202 can be supported in part by supportingmembers 1214A, 1214B. The pressure sensor 1200 can define a cavity 1216,e.g., filled with air.

As seen in the example of FIG. 12C, the sensor membrane 1206 can includea portion 1218 that can extend inwardly toward a center of the pressuresensor 1204 and that can taper, such as to a point. The portion 1218 canfocus the response of the membrane 1206 against the area between FBG 1and FBG 2, such as for thereby further concentrating a stress in thephase-shift region, which can enhance the sensitivity of the pressuresensor 1200.

A portion of the supporting member 1214 can define a reservoir 1220,such as laterally below the area extending axially between FBG 1 and FBG2. The reservoir 1220 can further enhance the sensitivity of thepressure sensor 1200, such as by allowing the area between FBG 1 and FBG2 to deflect into the reservoir 1220.

In the example shown in FIG. 12C, the flexible sensor membrane 1206 caninclude, for example, a thin polymer film, a heat seal film, or a thinmetal foil. The flexible sensor membrane 1206 can be attached to thepressure sensor 1200, such as via bonding or solder. In an example, themembrane 1206 can be made by casting a silicone layer.

The pressure sensor 1200 can be sealed, such as on both the proximal end1222 and the distal end 1224. The sensor membrane 1206 can be sealed,such as for creating the sealed cavity 1216.

The example of a pressure sensor 1200 of FIG. 12C can include two FBGs(e.g., Fabry-Perot gratings FBG 1 and FBG 2), which can be used to sensechanges in pressure, such as described above with respect to FIG. 10D.The pressure sensor 1200 can optionally further include one or moretemperature compensating FBGs. For example, the pressure sensor 1200 caninclude two additional FBGs (e.g., FBGs 3 and 4 of FIG. 10D), which canform a phase-shifted FBG structure, such as for sensing temperature. Thechange in phase-shift between FBG 3 and FBG 4 can be quantified and thechange in temperature can be determined from the quantified phase-shift,such as described above.

FIGS. 13A-13C depict an example of a guidewire in combination with anoptical pressure sensor. FIG. 13A is an example of a perspective viewillustrating a combination 1300 of a guidewire 1302 and an optical fiber1304 attached to an optical fiber pressure sensor. An optical fiberpressure sensor can be attached at a distal end of the guidewire 1302.The optical fiber 1304 can be disposed in a smooth, rounded groove(groove 1306 of FIG. 13C) extending axially along an outer diameter ofthe guidewire 1302 and optionally helically wound about the guidewire1302, such as within a helically axially extending groove. FIG. 13B isan example of a cross-sectional side view of the combination 1300 ofFIG. 13A, illustrating the optional helical pitch of the combination.

FIG. 13C is an example of a cross-sectional end view of the combination1300 of FIG. 13A, such as can be taken along section A-A of FIG. 13B.The guidewire 1302 can include a solid guidewire with a smooth, roundedgroove 1306 etched out, for example, of the guidewire material (oretched out of a coating thereupon), thereby preserving most of theguidewire material, which can help preserve its mechanical properties.In this manner, the guidewire can be substantially solid, which canavoid the kinking issues that can be associated with hollow guidewires.Using a substantially solid guidewire can improve the guidewire's torquecapabilities. In an example, a coating can be applied over the guidewire1302 and over the fiber 1304, such as to help protect the fiber 1304 orto help secure the fiber 1304 to the guidewire 1302.

FIGS. 14A-14C depict an example of a guidewire in combination with anoptical fiber pressure sensor. FIG. 14A is an example of a perspectiveview illustrating a combination 1400 of a guidewire 1402 and an opticalfiber 1404 that can be attached to an optical fiber pressure sensor. Anoptical fiber pressure sensor can be attached at a distal end of theguidewire 1402. The optical fiber 1402 can be disposed in a flat groove(flat groove 1406 of FIG. 14C) extending axially along an outer diameterof the guidewire 1402 (or along a coating thereupon) and optionallyhelically wound about the guidewire 1402. FIG. 14B is a cross-sectionalside view of the combination 1400 of FIG. 14A, illustrating the helicalpitch of the combination. The helical design can allow any stresses,e.g., from compression and tension, to be more evenly distributed alongthe length of the guidewire.

FIG. 14C is a cross-sectional end view of the combination 1400 of FIG.14A, such as can be taken along section A-A of FIG. 14B. The guidewire1402 can include a solid guidewire with a flat groove 1406 etched out,for example, of the guidewire material, or a coating thereupon, therebypreserving most of the guidewire material and the mechanical propertiesassociated therewith. In this manner, the guidewire can be substantiallysolid, which can help avoid the kinking issues that can be associatedwith hollow guidewires. Using a substantially solid guidewire canprovide better torque capability of the guidewire. In an example, acoating can be applied over the guidewire 1402 and the fiber 1404, suchas to help protect the fiber 1404 or to help secure the fiber 1404 tothe guidewire 1402.

FIGS. 15A-15C depict an example of a guidewire in combination with anoptical fiber pressure sensor. FIG. 15A is an example of a perspectiveview illustrating a combination 1500 of a multifilar guidewire 1502 andan optical fiber 1504 that can be attached to an optical fiber pressuresensor. An optical fiber pressure sensor can be attached at a distal endof the guidewire 1502. The optical fiber 1504 can be disposed in aninterstice between filaments of the multifilar guidewire 1502 andoptionally axially helically wound about the guidewire 1502. FIG. 15B isan example of a cross-sectional side view of the combination 1500 ofFIG. 15A, illustrating an example of the helix pitch of the combination.

FIG. 15C is an example of a cross-sectional end view of the combination1500 of FIG. 15A, such as can be taken along section A-A of FIG. 15B.The multifilar guidewire 1502 can include multiple filaments 1506. Theoptical fiber 1504 can be disposed in an interstice between twofilaments 1506, for example, toward an outer diameter of the guidewire1502. In this manner, the guidewire can be substantially rigid, like asolid guidewire, which can help avoid the kinking issues that can beassociated with hollow guidewires. Using a substantially solid guidewirecan help provide desired torque capability of the guidewire. In anexample, a coating can be applied over the guidewire 1502 and the fiber1504, such as to help protect the fiber 1504 or to help secure the fiber1504 to the guidewire 1502.

FIG. 16 depicts another example of a pressure sensor that can be used toimplement various techniques of this disclosure. The example of apressure sensor depicted in FIG. 16 can provide an example of anintegrated pressure sensor that can use one or more Fabry-Perot gratingarrangements. Again, an “integrated” pressure sensor can involve placingthe fiber with the appropriate gratings written in the fiber on aguidewire and then completing the sensor once the fiber is positioned onthe wire.

FIG. 16 is an example of a perspective cross-sectional view of anoptical fiber pressure sensor 1600 that can include an optical fiber1602 that can be configured to transmit one or more optical sensingsignals and a temperature compensated Fiber Bragg Grating (FBG)interferometer 1604 in optical communication with the optical fiber1602. The FBG interferometer 1604 can be configured to receive pressure,e.g., from pressure waves, and to modulate, in response to the receivedpressure, the optical sensing signal. The pressure sensor 1600 caninclude a sensor membrane 1606 that can be in physical communicationwith the FBG interferometer 1604. The sensor membrane 1606 can beconfigured to transmit the pressure to the FBG interferometer 1604.

The example of a pressure sensor 1600 of FIG. 16 can further includeFabry-Perot gratings FBG 1 and FBG 2, which can be used to sense changesin pressure. The Fabry-Perot gratings FBG 1 and FBG 2 can create a phaseshift that can be tracked in a manner similar to that described above.

The pressure sensor 1600 of FIG. 16 can further include a proximal coil1608 and a distal coil 1610. The proximal and distal coils 1608, 1610can provide flexibility to aid advancement of the pressure sensor 1600through tortuous pathways. In one example, the proximal and distal coils1608, 1610 can be affixed together via a mechanical joint (notdepicted), e.g., via solder or adhesive. The FBG interferometer 1604can, in some examples, be positioned underneath the mechanical joint toprovide additional protection to the FBG interferometer 1604.

The pressure sensor 1600 of FIG. 16 can further include a guidewire 1612to which the optical fiber 1602 can be attached. In the example depictedin FIG. 16, a portion of the guidewire 1612 can define a machined gap(not depicted) underneath the proximal coil 1608. The machined gap canallow the optical fiber 1602 to extend longitudinally or helically alongthe outer surface of the guidewire 1612 and then transition underneaththe proximal coil gradually into the machined gap.

The guidewire 1612 can also define cavity 1614, e.g., filled with air,laterally below the sensor membrane 1606. The sensor membrane 1606 andthe cavity 1614 can concentrate a stress in the area between theFabry-Perot gratings FBG 1 and FBG 2, which can enhance the sensitivityof the pressure sensor 1600. The optical fiber 1602 can be securelyattached to the guidewire 1612 on each side of the cavity 1614. Inaddition, the sensor membrane 1606 can be sealed 360 degrees around theguidewire 1612 at an optical fiber entry end 1616 of the sensor membrane1606 and at a distal end 1618 of the optical fiber 1602 and along theedges of the membrane 1606.

FIG. 17 depicts another example of a pressure sensor that can be used toimplement various techniques of this disclosure. FIG. 17 depicts anotherexample of a pressure sensor that can be used to implement varioustechniques of this disclosure. The example of a pressure sensor 1700depicted in FIG. 17 can provide an example standalone pressure sensorthat can use one or more Fabry-Perot grating arrangements.

FIG. 17 is an example of a perspective cross-sectional view of anoptical fiber pressure sensor 1700 that can include an optical fiber1702 that can be configured to transmit one or more optical sensingsignals and a temperature compensated Fiber Bragg Grating (FBG)interferometer 1704 in optical communication with the optical fiber1702. The FBG interferometer 1704 can be configured to receive pressure,e.g., from pressure waves, and to modulate, in response to the receivedpressure, the optical sensing signal. The pressure sensor 1700 caninclude a sensor membrane 1706 that can be in physical communicationwith the FBG interferometer 1704. The sensor membrane 1706 can beconfigured to transmit the pressure to the FBG interferometer 1704.

The example of a pressure sensor 1700 of FIG. 17 can include four FBGs(e.g., FBGs 1-4.) FBGs 3 and 4 can form a phase-shifted FBG structure,such as for sensing temperature. The change in phase-shift between FBG 3and FBG 4 can be detected and quantified, and the change in temperaturecan be determined from the quantified phase-shift, such as describedabove.

The pressure sensor 1700 can further include Fabry-Perot gratings FBG 1and FBG 2, which can be used to sense changes in pressure. Similar tothe phase-shift grating structures described above with respect to FIG.10D, the Fabry-Perot gratings FBG 1 and FBG 2 can create a phase shiftthat can be tracked in a manner similar to that described above. Thatis, a notch can be created in the wavelength response to the Fabry-Perotgratings FBG 1 and FBG 2, as shown and described in detail above. Apoint on a slope of the notch can be set and tracked, a phase shift canbe detected and quantified, and the change in pressure can be determinedfrom the quantified phase-shift, such as described in detail above.

The pressure sensor 1700 of FIG. 17 can further include a proximal coil1708 and a distal coil 1710. The proximal and distal coils 1708, 1710can provide additional flexibility to aid advancement of the pressuresensor 1700 through tortuous pathways. In one example, the proximal anddistal coils 1708, 1710 can be affixed together via a mechanical joint1712, e.g., via solder or adhesive. The FBG interferometer 1704 can, insome examples, be positioned underneath the mechanical joint 1712 toprovide additional protection to the FBG interferometer 1704.

The pressure sensor 1700 of FIG. 17 can further include a guidewire 1714to which the FBG interferometer 1704 can be attached. In the exampledepicted in FIG. 17, a portion of the guidewire can define a machinedgap 1716 underneath a portion of the proximal coil 1708 and the distalcoil 1710. The machined gap 1716 can allow the optical fiber 1702 toextend longitudinally or helically along the outer surface of theguidewire 1714 and then transition underneath the proximal coil 1708gradually into the machined gap 1716.

The example of a pressure sensor 1700 in FIG. 17 can include acantilevered design, which can be applied to any of the examples ofstandalone pressure sensors described in this disclosure. Moreparticularly, the pressure sensor 1700 can include a cantilever tube1718 that is disposed about a distal portion of the optical fiber 1702within the machined gap 1716. In addition, the pressure sensor 1700 caninclude a sensor tube 1720 disposed within the cantilever tube 1718 andabout the distal portion of the optical fiber 1702. To provide supportto a portion of the optical fiber 1702, the pressure sensor 1700 canalso include a fiber support 1722 that is positioned between the sensortube 1720 and a portion of the optical fiber 1702.

Between a portion of an inner surface of the cantilever tube 1718 and anouter surface of the sensor tube 1720, the pressure sensor 1700 candefine a space 1724, thereby providing a double-walled housingconstruction. The double-walled housing construction and the space 1724can allow the outer surface of the sensor tube 1720 to be mounted to theguidewire 1714 while isolating the FBG interferometer 1704 from motionof the guidewire 1714 and contact with the proximal coil 1708.

The FBG interferometer 1704 can also define cavity 1726, e.g., filledwith air, laterally below the sensor membrane 1706 and a portion of theoptical fiber 1702 and within the region defined by the sensor tube1720. The sensor membrane 1706 and the cavity 1726 can concentrate astress in the area between the Fabry-Perot gratings FBG 1 and FBG 2,which can enhance the sensitivity of the pressure sensor 1700.

FIG. 18 depicts another example of a pressure sensor that can be used toimplement various techniques of this disclosure. The example of apressure sensor depicted in FIG. 18 can provide an example of anintegrated pressure sensor that can use one or more Fabry-Perot gratingarrangements.

FIG. 18 is an example of a perspective cross-sectional view of anoptical fiber pressure sensor 1800 that can include an optical fiber1802 that can be configured to transmit one or more optical sensingsignals and a temperature compensated Fiber Bragg Grating (FBG)interferometer 1804 in optical communication with the optical fiber1802. The FBG interferometer 1804 can be configured to receive pressure,e.g., from pressure waves, and to modulate, in response to the receivedpressure, the optical sensing signal. The pressure sensor 1800 caninclude a sensor membrane 1806 that can be in physical communicationwith the FBG interferometer 1804. The sensor membrane 1806 can beconfigured to transmit the pressure to the FBG interferometer 1804.

The pressure sensor 1800 of FIG. 18 can further include a proximal coil1808 and a distal coil 1810. The proximal and distal coils 1808, 1810can provide additional flexibility to aid advancement of the pressuresensor 1800 through tortuous pathways. In one example, the proximal anddistal coils 1808, 1810 can be affixed together via a mechanical joint1812, e.g., via solder or adhesive. The FBG interferometer 1804 can, insome examples, be positioned underneath the mechanical joint 1812 toprovide additional protection to the FBG interferometer 1804.

The pressure sensor 1800 of FIG. 18 can further include a guidewire 1814to which the FBG interferometer 1804 can be attached. In the exampledepicted in FIG. 18, a portion of the guidewire 1814 can define amachined gap 1816 underneath a portion of the proximal coil 1808 and thedistal coil 1810. The machined gap 1816 can allow the optical fiber 1802to extend longitudinally or helically along the outer surface of theguidewire 1814 and then transition underneath the proximal coil 1808gradually into the machined gap 1816.

The example of a pressure sensor 1800 in FIG. 18 can include a capillarytube design. More particularly, the pressure sensor 1800 can include acapillary tube 1818 to support a portion of the optical fiber 1802. Thecapillary tube 1818 can be disposed about a distal portion of theoptical fiber 1802 within the machined gap 1816.

As seen in FIG. 18, a portion 1817 of the optical fiber 1802 can extendbeyond a distal end of the capillary tube 1818 and over a cavity 1820,e.g., filled with air, that is laterally below the portion of theoptical fiber 1802 that extends beyond the distal end of the capillarytube 1818. The example of a pressure sensor 1800 of FIG. 18 can includeat least three FBGs (e.g., FBGs 1-3.) FBG 1 can be configured to beindependent of pressure and can be used for temperature measurement,such as to provide a temperature compensated optical fiber pressuresensor, such as described above with respect to FIG. 3 and FIG. 4A.

FBGs 2 and 3 can form a phase-shift FBG structure. The surface area ofthe membrane 1806 can concentrate a change in pressure and can focus amechanical response to the change in pressure at the phase-shift regionbetween FBG 2 and FBG 3. This focused mechanical response can enhancethe sensitivity of the pressure sensor 1800. The mechanical forcesacting upon the phase-shift region between FBG 2 and FBG 3 canconcentrate a stress in the phase-shift region. The concentrated stressin the phase-shift region can change the refractive index of the opticalfiber 1802, which, in turn, alters the phase relationship between FBG 2and FBG 3. The change in phase-shift between FBG 2 and FBG 3 can bedetected and quantified, and the change in pressure can be determinedfrom the quantified phase-shift.

As seen in FIG. 18, the sensor membrane 1806 can be disposed about theguidewire 1814, the capillary tube 1818, and the portion of the opticalfiber that extends beyond the distal end of the capillary tube 1818.

FIG. 19 depicts another example of a pressure sensor that can be used toimplement various techniques of this disclosure. FIG. 19 depicts anotherexample of a pressure sensor that can be used to implement varioustechniques of this disclosure. The example of a pressure sensor 1900depicted in FIG. 19 can provide an example standalone pressure sensorthat can use one or more Fabry-Perot grating arrangements.

FIG. 19 is an example of a perspective cross-sectional view of anoptical fiber pressure sensor 1900 that can include an optical fiber1902 that can be configured to transmit one or more optical sensingsignals and a temperature compensated Fiber Bragg Grating (FBG)interferometer 1904 in optical communication with the optical fiber1902. The FBG interferometer 1904 can be configured to receive pressure,e.g., from pressure waves, and to modulate, in response to the receivedpressure, the optical sensing signal.

The example of a pressure sensor 1900 of FIG. 19 can include four FBGs(e.g., FBGs 1-4.) FBGs 3 and 4 can form a phase-shifted FBG structure,such as for sensing temperature. The change in phase-shift between FBG 3and FBG 4 can be detected and quantified, and the change in temperaturecan be determined from the quantified phase-shift, such as describedabove.

The pressure sensor 1900 can further include Fabry-Perot gratings FBG 1and FBG 2, which can be used to sense changes in pressure. Similar tothe phase-shift grating structures described above with respect to FIG.10D, the Fabry-Perot gratings FBG 1 and FBG 2 can create a phase shiftthat can be tracked in a manner similar to that described above. Thatis, a notch can be created in the wavelength response to the Fabry-Perotgratings FBG 1 and FBG 2, as shown and described in detail above. Apoint on a slope of the notch can be set and tracked, a phase shift canbe detected and quantified, and the change in pressure can be determinedfrom the quantified phase-shift, such as described in detail above.

The pressure sensor 1900 of FIG. 19 can further include a proximal coil1906, a distal coil 1908, and a guidewire 1910. The proximal and distalcoils 1906, 1908 can provide additional flexibility to aid advancementof the pressure sensor 1900 through tortuous pathways.

The pressure sensor 1900 of FIG. 19 can further include a tubularhousing 1912 that can be disposed about the guidewire 1912 between theproximal and distal coils 1906, 1908. In one example, the proximal anddistal coils 1906, 1908 can be affixed to the housing 1912 viamechanical joints 1914A, 1914B, e.g., via solder or adhesive. Thehousing 1912 can be affixed to the guidewire 1910 via a mechanical joint1915.

In addition, the pressure sensor 1900 can include a sensor tube 1916disposed within the housing 1912 and disposed about a distal portion ofthe optical fiber 1902. More particularly, the sensor tube 1916 can bepositioned within an area machined out of a portion of the outer wall1918 of the housing 1912. To provide support to the optical fiber 1902,a fiber support 1920 can be disposed about the optical fiber 1902between the sensor tube 1916 and the optical fiber 1902.

To allow the received pressure to reach the optical fiber 1902, aportion of the sensor tube 1916 can be removed in order to define asensor window 1922. The sensor window 1922 can be covered with thesensor membrane 1924.

The example of a pressure sensor 1900 of FIG. 19 can include four FBGs(e.g., FBGs 1-4). FBGs 3 and 4 can form a phase-shifted FBG structure,such as for sensing temperature. The change in phase-shift between FBG 3and FBG 4 can be detected and quantified, and the change in temperaturecan be determined from the quantified phase-shift, such as describedabove.

The pressure sensor 1900 can further include Fabry-Perot gratings FBG 1and FBG 2, which can be used to sense changes in pressure. TheFabry-Perot gratings FBG 1 and FBG 2 can create a phase shift that canbe tracked in a manner similar to that described above. That is, a notchcan be created in the wavelength response to the Fabry-Perot gratingsFBG 1 and FBG 2, as shown and described in detail above. A point on aslope of the notch can be set and tracked, a phase shift can be detectedand quantified, and the change in pressure can be determined from thequantified phase-shift, such as described in detail above.

The pressure sensor 1900 can define a cavity 1926, e.g., filled withair, laterally below the sensor membrane 1924 and the optical fiber1902. The sensor membrane 1924 and the cavity 1926 can concentrate astress in the area between the Fabry-Perot gratings FBG 1 and FBG 2,which can enhance the sensitivity of the pressure sensor 1900.

FIG. 20 depicts another example of a pressure sensor that can be used toimplement various techniques of this disclosure. The example of apressure sensor 2000 depicted in FIG. 20 can provide an examplestandalone pressure sensor that can use one or more Fabry-Perot gratingarrangements.

FIG. 20 is an example of a perspective cross-sectional view of anoptical fiber pressure sensor 2000 that can include an optical fiber2002 that can be configured to transmit one or more optical sensingsignals and a temperature compensated Fiber Bragg Grating (FBG)interferometer 2004 in optical communication with the optical fiber2002. The FBG interferometer 2004 can be configured to receive pressure,e.g., from pressure waves, and to modulate, in response to the receivedpressure, the optical sensing signal.

The example of a pressure sensor 2000 of FIG. 20 can include four FBGs(e.g., FBGs 1-4.) FBGs 3 and 4 can form a phase-shifted FBG structure,such as for sensing temperature. The change in phase-shift between FBG 3and FBG 4 can be detected and quantified, and the change in temperaturecan be determined from the quantified phase-shift, such as describedabove.

The pressure sensor 2000 can further include Fabry-Perot gratings FBG 1and FBG 2, which can be used to sense changes in pressure. Similar tothe phase-shift grating structures described above with respect to FIG.10D, the Fabry-Perot gratings FBG 1 and FBG 2 can create a phase shiftthat can be tracked in a manner similar to that described above. Thatis, a notch can be created in the wavelength response to the Fabry-Perotgratings FBG 1 and FBG 2, as shown and described in detail above. Apoint on a slope of the notch can be set and tracked, a phase shift canbe detected and quantified, and the change in pressure can be determinedfrom the quantified phase-shift, such as described in detail above.

The pressure sensor 2000 of FIG. 20 can further include a proximal coil2006, a distal coil 2008, and a guidewire 2010. The proximal and distalcoils 2006, 2008 can provide additional flexibility to aid advancementof the pressure sensor 2000 through tortuous pathways. In one example,the proximal and distal coils 2006, 2008 can be affixed together via amechanical joint 2012, e.g., via solder or adhesive. The FBGinterferometer 2004 can, in some examples, be positioned underneath themechanical joint 2012 to provide additional protection to the FBGinterferometer 2004.

The pressure sensor 2000 of FIG. 20 can further include a tubularhousing 2014 that can be disposed about the guidewire 2010 andunderneath the mechanical joint 2012. The housing 2014 can be affixed tothe guidewire 2010 via a mechanical joint 2015. In addition, thepressure sensor 2000 can include a sensor tube 2016 disposed within thehousing 2014 and disposed about a distal portion of the optical fiber2002. In contrast to the tubular housing of FIG. 19, the tubular housing2014 of FIG. 20 can define a lumen 2018 that extends longitudinallythrough the housing 2014. The sensor tube 2016 of FIG. 20 can bepositioned within the lumen 2018. To provide support to the opticalfiber 2002, a fiber support 2020 can be disposed about the optical fiber2002 between the sensor tube 2016 and the optical fiber 2002.

To allow the received pressure to reach the optical fiber 2002, aportion of the sensor tube 2016 can be removed in order to define asensor window 2022. The sensor window 2022 can be covered with a sensormembrane 2024.

The example of a pressure sensor 2000 of FIG. 20 can include four FBGs(e.g., FBGs 1-4). FBGs 3 and 4 can form a phase-shifted FBG structure,such as for sensing temperature. The change in phase-shift between FBG 3and FBG 4 can be detected and quantified, and the change in temperaturecan be determined from the quantified phase-shift, such as describedabove.

The pressure sensor 2000 can further include Fabry-Perot gratings FBG 1and FBG 2, which can be used to sense changes in pressure. TheFabry-Perot gratings FBG 1 and FBG 2 can create a phase shift that canbe tracked in a manner similar to that described above. That is, a notchcan be created in the wavelength response to the Fabry-Perot gratingsFBG 1 and FBG 2, as shown and described in detail above. A point on aslope of the notch can be set and tracked, a phase shift can be detectedand quantified, and the change in pressure can be determined from thequantified phase-shift, such as described in detail above.

The pressure sensor 2000 can define a cavity 2026, e.g., filled withair, laterally below the sensor membrane 2024 and the optical fiber2002. The sensor membrane 2024 and the cavity 2026 can concentrate astress in the area between the Fabry-Perot gratings FBG 1 and FBG 2,which can enhance the sensitivity of the pressure sensor 2000.

FIGS. 21A-21D depict another example of a guidewire in combination withan optical fiber pressure sensor. FIG. 21A is an example of a partialcutaway view illustrating a combination 2100 of a guidewire 2102 and anoptical fiber 2104 attached to an optical fiber pressure sensor 2106(FIG. 21C).

In one example, the guidewire 2102 can be substantially similar to theguidewire shown and described in U.S. Pat. No. 5,341,818 to Abrams etal. and assigned to Abbott Cardiovascular Systems, Inc. of Santa Clara,Calif., the entire contents of which being incorporated herein byreference. The guidewire 2102 can include a proximal portion 2108 and adistal portion 2110. The distal portion 2110 can be formed at leastpartially of superelastic materials. The guidewire 2102 can furtherinclude a tubular connector 2112 that can connect a distal end 2114 ofthe proximal portion 2108 and a proximal end 2116 of the distal portion2110.

The guidewire 2102 can further include a core wire 2118 having anelongated portion 2120 and a tapered portion 2122 extending distallybeyond the elongated portion 2120. In addition, the guidewire 2102 caninclude a proximal coil 2124 disposed about the elongated portion 2120and a distal coil 2126 disposed about a portion of each of the elongatedportion 2120 and the tapered portion 2122 and extending distally beyondthe tapered portion 2122. The proximal coil 2124 and the distal coil2126 can be joined together via a mechanical joint 2128, e.g., solder oradhesive. The guidewire 2102 can further include a distal plug 2130,about which a portion of the distal coil 2126 can be wound, or aconventional solder tip. Additional information regarding the componentsand construction of the guidewire 2102 can be found in U.S. Pat. No.5,341,818.

Regarding construction of the combination 2100 of the guidewire 2102 andthe optical fiber 2104 attached to an optical fiber pressure sensor 2106(FIG. 21C), in one example, a narrow, shallow channel or groove 2132(FIG. 21B) can be cut into the outer wall of the components that formthe guidewire 2102, e.g., the core wire 2118 and the tubular connector2112. The optical fiber 2104 can be positioned within the groove 2132.Due to the relatively small dimensions of optical fiber 2104, thedimensions of the groove 2132 can have minimal impact on the performanceof the guidewire 2102.

The groove 2132 can extend along the length of the guidewire 2102substantially parallel to a longitudinal axis of the guidewire 2102. Inanother example, the groove 2132 can spiral about the guidewire 2102,e.g., a helically axially extending groove. In other examples, thegroove 2132 can extend along a portion of the length of the guidewire2102 substantially parallel to a longitudinal axis of the guidewire 2102and then the groove 2132 can spiral about another portion of the lengthof the guidewire 2102, e.g., a helically axially extending groove. Thepitch of the spiral can be varied along the length of the guidewire.

The groove 2132 can be fabricated using various techniques that include,but are not limited to, etching, machining, and laser ablation. Inaddition, the groove 2132 can be fabricated at various stages during theconstruction of the guidewire 2102, e.g., before or after applying acoating to the guidewire 2102.

The optical fiber 2104 can be bonded to the groove 2132 using varioustechniques. For example, the optical fiber 2104 can be bonded to thegroove 2132 by applying a hot melt adhesive to the optical fiber 2104prior to positioning the optical fiber 2104 in the groove 2132 and thensubsequently applying heat.

In other examples, rather than a groove 2132 that is cut into the outerwall of the components that form the guidewire 2102, the guidewire 2102can define a lumen (not depicted) that extends along a portion of thelength of the guidewire 2102 substantially parallel to a longitudinalaxis of the guidewire 2102. The lumen can be coaxial with thelongitudinal axis of the guidewire 2102, or the lumen can be radiallyoffset from the longitudinal axis of the guidewire 2102. The opticalfiber 2104 can extend along the length of the guidewire 2102 through thelumen. The dimensions of the lumen can have minimal impact on theperformance of the guidewire 2102.

In another example, the guidewire 2102 can be constructed to include anannular gap (not depicted) between the proximal coil 2124 and theelongated portion 2120. The optical fiber 2104 can then extend along thelength of the elongated portion 2120 between an outer surface of theelongated portion 2120 and an inner surface of the proximal coil 2124.The optical fiber 2104 can be wound about the elongated portion 2120. Insome examples, the optical fiber 2104 can be secured to the elongatedportion 2120, e.g., via an adhesive.

FIG. 21B is an example of a cross-sectional view of the combination 2100of FIG. 21A, such as taken along section B-B of FIG. 21A. The guidewire2102, e.g., a solid guidewire, can include the fabricated groove 2132.FIG. 21B illustrates the optical fiber 2104 positioned within the groove2132 of the core wire 2118 of the guidewire 2102.

FIG. 21C is an example of a cross-sectional view of the combination 2100of FIG. 21A, such as taken along section E-E of FIG. 21A. Moreparticularly, FIG. 21C depicts another example of a pressure sensor 2106that can be used to implement various techniques of this disclosure.

The optical fiber pressure sensor 2106 can include the optical fiber2104 that can be configured to transmit one or more optical sensingsignals and a temperature compensated Fiber Bragg Grating (FBG)interferometer 2134 in optical communication with the optical fiber2104. The FBG interferometer 2134 can be configured to receive pressure,e.g., from pressure waves, and to modulate, in response to the receivedpressure, the optical sensing signal.

The example of a pressure sensor 2106 of FIG. 21C can further includeFBGs (not depicted) similar to those described in detail above withrespect to various examples of pressure sensors, e.g., FIG. 10D, whichcan be used to sense changes in pressure. The FBGs can create a phaseshift that can be tracked in a manner similar to that described above.

The pressure sensor 2106 of FIG. 21C can further include the proximalcoil 2124 and the distal coil 2126. The proximal and distal coils 2124,2126 can provide flexibility to aid advancement of the pressure sensor2106 through tortuous pathways. In one example, the proximal and distalcoils 2124, 2126 can be affixed together via a mechanical joint 2136.The FBG interferometer 2134 can, in some examples, be positionedunderneath the mechanical joint 2136 to provide additional protection tothe FBG interferometer 2134.

As indicated above, the guidewire 2102 can be fabricated with a groove2132 (FIG. 21B) to which the optical fiber 2104 can be attached. Aportion of the optical fiber 2104 can extend underneath the mechanicaljoint 2136. To allow the received pressure to reach the optical fiber2104, a portion of the mechanical joint 2136 can be removed in order todefine a sensor window, shown generally at 2138. The sensor window 2138can be covered with the sensor membrane 2140.

In the example depicted in FIG. 21C, the pressure sensor 2106 can beconstructed by fabricating a small cavity 2142 in the core wire 2118that is in communication with the groove 2132 at the distal end of theoptical fiber 2104. The cavity 2142 can, for example, be 100 microns indiameter by 100 microns in depth. The guidewire 2102 can be constructedof the superelastic material, or a different super stiff material may besubstituted at this location (not depicted), for example, aluminum oxide(Al₂O₃) or Alumina ceramic which can be precision molded to define thecavity 2142 and the groove 2132.

The pressure sensor 2106 can further include a microballoon 2144 placedinto the cavity 2142. In some examples, an adhesive (not depicted) canbe placed in the cavity 2142 to secure the microballoon 2144 in place.The microballoon 2144 can be filled with a gas, sealed, and heatexpanded such that, when expanded, the microballoon 2144 can fill thecavity 2142 and maintain a sealed reference chamber. If an upper surfaceof the microballoon 2144 is constricted during its expansion, a flatdiaphragm can be achieved. The optical fiber 2104 with FBGs can bepositioned in the groove 2132 and across the flat diaphragm of themicroballoon 2144.

The remaining space of the cavity 2142 and the groove 2132 can be filledwith an adhesive (not depicted) such as silicone to capture the opticalfiber 2104, to attach the optical fiber 2104 to the guidewire 2102, toattach the optical fiber 2104 to the microballoon 2144, and to define arelatively thin silicone diaphragm in mechanical communication with thechamber defined by the microballoon 2144 where the optical fiber 2104 isembedded. As a pressure is applied, each of the silicone, the opticalfiber 2104, and the microballoon 2144 can flex due to compression of thesealed chamber. The flexing can transmit the received pressure to theFBG interferometer 2134, which can create a responsive phase shiftbetween FBGs (not depicted) that can be tracked in a manner similar tothat described above.

FIG. 21D is an example of a cross-sectional view of the combination 2100of FIG. 21A, such as taken along section A-A of FIG. 21A. Moreparticularly, FIG. 21D depicts a cross-sectional view of the pressuresensor 2106 of FIG. 21C. As seen in FIG. 21D and as described above withrespect to FIG. 21C, the pressure sensor 2106 of FIG. 21C can includethe microballoon 2144 positioned within the cavity 2142. The opticalfiber 2104 with FBGs can be positioned in the groove 2132 and across theflat diaphragm 2146 of the microballoon 2144.

Any of optical fiber pressure sensors described in this disclosure canbe combined with the guidewire 2102 shown and described above withrespect to FIG. 21A and in U.S. Pat. No. 5,341,818. Further, thetechniques of this disclosure are not limited to the use of a singlesensor in combination with a guidewire, e.g., guidewire 2102. Rather,two or more sensors, e.g., pressure sensors, can be combined with aguidewire by defining sensor regions in which each of the two or moresensors can function at a respective, unique wavelength and can beaddressed accordingly by a laser matching the wavelength of therespective sensor. Each laser can be multiplexed onto the optical fiberusing standard techniques, e.g., wavelength-division multiplexing (WDM),found in telecommunications systems.

In another example, the guidewire 2102 of FIG. 21A can be combined withother sensor techniques. For example, the same guidewire can be used forboth intravascular ultrasound (IVUS) imaging and pressure sensing byusing the imaging sensor configurations described in U.S. Pat. No.7,245,789 to Bates et al., and assigned to Vascular Imaging Corp, theentire contents of which being incorporate herein by reference. By wayof specific example, one of the optical fibers in a 32 fiber arrangementcan extend distally beyond an imaging sensor region, where an opticalfiber pressure sensor, such as any of the optical fiber pressure sensorsdescribed in this disclosure, can be included that utilizes a differentwavelength than that used by the imaging arrangement.

FIG. 22 depicts an example of a combination 2200 of a guidewire 2202with an optical fiber pressure sensor 2204 and an imaging sensor 2206,e.g., using the imaging sensor configurations described in U.S. Pat. No.7,245,789. In particular, FIG. 22 is an example of a perspective partialcutaway view of the combination 2200.

The guidewire 2202 is similar in construction to the guidewire 2102described above with respect to FIG. 21A, and as shown and described inU.S. Pat. No. 5,341,818. The guidewire 2202 can include a core wire2208, a proximal coil 2210, and a distal coil 2212.

The imaging sensor 2206 can include an optical fiber ribbon 2214 havinga plurality of optical fibers, e.g., 32 optical fibers, disposed aboutthe core wire 2208 of the guidewire 2202, and a plurality of imaginggratings 2216 to couple light into and/or out of one or more respectiveoptical fibers of the ribbon 2214.

The guidewire 2202 can further include a backing 2218 disposed about thecore wire 2208 and positioned between the core wire 2208 and the opticalfiber ribbon 2214. In addition, the guidewire 2202 can include amechanical joint 2220 for joining a proximal portion 2222 of theguidewire 2202 to a distal portion 2224 of the guidewire 2202.

In one example, the pressure sensor 2204 can be similar to the pressuresensor 2106 of FIG. 21C. For purposes of conciseness, the pressuresensor 2204 will not be described in detail again. The pressure sensor2204 can include a single optical fiber 2226 that extends longitudinallyalong the length of the guidewire 2202, e.g., within a groove in theouter surface of the core wire 2208 and underneath the optical fiberribbon 2214. The pressure sensor 2204 can further include a pressuresensing window 2228 and pressure sensor membrane 2230, as described indetail above. The pressure sensor 2204 of FIG. 22 is not limited to thedesign of the pressure sensor 2106 of FIG. 21C. Rather, any of thepressure sensor configurations described in this disclosure can beapplied to the combination 2200.

In one example, an outer diameter of the guidewire 2202 can be reducedalong the length of the guidewire 2202 up to the distal coil 2212 toallow the optical fiber ribbon 2214 to be disposed about the outersurface of the guidewire 2202. By way of specific example, the outerdiameter of the proximal coil 2210 can be reduced from 0.014″ to 0.011″and the pressure sensor 2204 can be incorporated with the guidewire 2202either in a surface groove or a coaxial hole of the core wire 2208. Theoptical fiber ribbon 2214, e.g., a 32 optical fiber arrangement, of theimaging sensor 2206 can then be positioned over the 0.011″ outerdiameter of the guidewire 2202 so that the assembly contains 33 opticalfibers, for example. This configuration can separate the multiplexingrequirements of the imaging sensor 2206 and the pressure sensor 2204,and can allow the pressure sensor 2204 to operate at any wavelength,including that of the imaging sensor 2206.

FIGS. 23A-23B depict another example of a guidewire in combination withan optical fiber pressure sensor. FIG. 23A is an example of a partialcutaway view illustrating a combination 2300 of a guidewire 2302 and anoptical fiber 2304 attached to an optical fiber pressure sensor 2306(FIG. 23B).

The guidewire 2302 can include a proximal portion 2308 and a distalportion 2310. The distal portion 2310 can be formed at least partiallyof superelastic materials. The guidewire 2302 can further include atubular connector 2312 that can connect a distal end 2314 of theproximal portion 2308 and a proximal end 2316 of the distal portion2310.

The guidewire 2302 can further include a core wire 2318 having anelongated portion 2320 and a tapered portion 2322 extending distallybeyond the elongated portion 2320. In addition, the guidewire 2302 caninclude a proximal coil 2324 disposed about the elongated portion 2320and the tapered portion 2322. The guidewire 202 can also include adistal coil 2326 disposed about a portion of the tapered portion 2322and extending distally beyond the tapered portion 2322. The proximalcoil 2324 and the distal coil 2326 can be joined together via amechanical joint 2328, e.g., solder or adhesive. The guidewire 2302 canfurther include a distal plug 2330, about which a portion of the distalcoil 2326 can be wound, or a conventional solder tip.

Regarding construction of the combination 2300 of the guidewire 2302 andthe optical fiber 2304 attached to an optical fiber pressure sensor2306, in one example, a narrow, shallow channel or groove (not depicted)can be cut into the outer wall of the components that form the guidewire2302, e.g., the core wire 2318 and the tubular connector 2312. Theoptical fiber 2304 can be positioned within the groove. Due to therelatively small dimensions of optical fiber 2304, the dimensions of thegroove can have minimal impact on the performance of the guidewire 2302.

The groove can extend along the length of the guidewire 2302substantially parallel to a longitudinal axis of the guidewire 2302. Inanother example, the groove can spiral about the guidewire 2302, e.g., ahelically axially extending groove. In other examples, the groove canextend along a portion of the length of the guidewire 2302 substantiallyparallel to a longitudinal axis of the guidewire 2302 and then thegroove can spiral about another portion of the length of the guidewire2302, e.g., a helically axially extending groove. The pitch of thespiral can be varied along the length of the guidewire.

The groove can be fabricated using various techniques that include, butare not limited to, etching, machining, and laser ablation. In addition,the groove can be fabricated at various stages during the constructionof the guidewire 2302, e.g., before or after applying a coating to theguidewire 2302.

The optical fiber 2304 can be bonded to the groove using varioustechniques. For example, the optical fiber 2304 can be bonded to thegroove by applying a hot melt adhesive to the optical fiber 2304 priorto positioning the optical fiber 2304 in the groove and thensubsequently applying heat.

The guidewire 2302 can be constructed to include an annular gap, shownin FIG. 23B at 2332, between the proximal coil 2324 and the portions2320, 2322. The optical fiber 2304 can then extend along the length ofthe portions 2320, 2322 of the distal portion 2310 between an outersurface of the portions and an inner surface of the proximal coil 2324.The optical fiber 2304 can be wound about the elongated portion 2320. Insome examples, the optical fiber 2304 can be secured to the elongatedportion 2320, e.g., via an adhesive.

The combination 2300 can further include a sleeve 2334 disposed aboutthe core wire 2318 and underneath the mechanical joint 2328, to receivea distal portion of the optical fiber 2304. In one example, sleeve 2334can be constructed of aluminum oxide (Al₂O₃), or other stiff material.The core wire 2318 can taper as it extends underneath the mechanicaljoint.

FIG. 23B is an example of a partial cutaway view of a portion of thecombination 2300 of FIG. 23A. More particularly, FIG. 23B depictsanother example of a pressure sensor 2306 that can be used to implementvarious techniques of this disclosure.

The optical fiber pressure sensor 2306 can include the optical fiber2304 that can be configured to transmit one or more optical sensingsignals and a temperature compensated Fiber Bragg Grating (FBG)interferometer 2334 in optical communication with the optical fiber2304. The FBG interferometer 2334 can be configured to receive pressure,e.g., from pressure waves, and to modulate, in response to the receivedpressure, the optical sensing signal.

The example of a pressure sensor 2306 of FIG. 23B can further includeFBGs (not depicted) similar to those described in detail above withrespect to various examples of pressure sensors, e.g., FIG. 10D, whichcan be used to sense changes in pressure. The FBGs can create a phaseshift that can be tracked in a manner similar to that described above.

The pressure sensor 2306 of FIG. 23B can further include the proximalcoil 2324 and the distal coil 2326. The proximal and distal coils 2324,2326 can provide flexibility to aid advancement of the pressure sensor2306 through tortuous pathways. In one example, the proximal and distalcoils 2324, 2326 can be affixed together via a mechanical joint 2328.The FBG interferometer 2334 can, in some examples, be positionedunderneath the mechanical joint 2328 to provide additional protection tothe FBG interferometer 2334.

As indicated above, the guidewire 2302 can be constructed to include anannular gap 2332 between the proximal coil 2324 and the portion 2320 toallow the optical fiber 2304 to extend along the length of the portion2320. The sleeve 2334 can include a lumen, groove, or pocket to receivethe distal end of the optical fiber 2304. To allow the received pressureto reach the optical fiber 2304, a portion of the mechanical joint 2328and the sleeve 2334 can be removed in order to define a sensor window,shown generally at 2338. The sensor window 2338 can be covered with thesensor membrane 2340.

In the example depicted in FIG. 23B, the pressure sensor 2306 can beconstructed by fabricating a small cavity 2342 in the core wire 2318.The cavity 2342 can, for example, be 100 microns in diameter by 100microns in depth. The guidewire 2302 can be constructed of thesuperelastic material, or a different super stiff material may besubstituted at this location (not depicted), for example, Al₂O₃, orAlumina ceramic which can be precision molded to define the cavity 2342.

The pressure sensor 2306 can further include a microballoon 2344 placedinto the cavity 2342. In some examples, an adhesive (not depicted) canbe placed in the cavity 2342 to secure the microballoon 2344 in place.The microballoon 2344 can be filled with a gas, sealed, and heatexpanded such that, when expanded, the microballoon 2344 can fill thecavity 2342 and maintain a sealed reference chamber. If an upper surfaceof the microballoon 2344 is constricted during its expansion, a flatdiaphragm can be achieved. The optical fiber 2304 with FBGs can bepositioned in the sleeve 2334 and across the flat diaphragm of themicroballoon 2344.

As a pressure is applied, the optical fiber 2304 and the microballoon2344 can flex due to compression of the sealed chamber. The flexing cantransmit the received pressure to the FBG interferometer 2334, which cancreate a responsive phase shift between FBGs (not depicted) that can betracked in a manner similar to that described above.

FIG. 24 shows an example of a portion of a concentric pressure sensorassembly 2400. The concentric pressure sensor assembly 2400 can includeor be coupled to an optical fiber 2402, such as a reduced-diameterlongitudinally extending central optical fiber 2402. The concentricpressure sensor assembly 2400 can be located at or near a distal regionof the optical fiber 2402. In an example, the pressure sensor assembly2400 can include at least one Fabry-Perot interferometer, such as in theoptical fiber 2402. The Fabry-Perot interferometer can modulate thewavelength of light in the optical fiber 2402, such as in response toenvironmental pressure variations that can stretch or compress theoptical fiber 2402, e.g., longitudinally and linearly. The modulatedlight in the optical fiber 2402 can be used to communicate informationabout the environmental pressure variations at or near the distal end ofthe optical fiber 2402 to a proximal end of the optical fiber 2402, suchas for coupling the resulting optical signal to an optoelectronic orother optical detector, which, in turn, can be coupled to electronic oroptical signal processing circuitry, such as for extracting orprocessing the information about the sensed environmental pressurevariations.

A distal portion of the optical fiber 2402 (e.g., more distal than theone or more Fabry-Perot interferometers) can be securely captured,anchored, or affixed, such as at a hard, solid, or inelastic distal diskassembly, distal endcap, or other distal anchor 2404, such as can belocated at a distal end portion of the concentric pressure sensorassembly 2400. The hard, solid, or inelastic material (e.g., fusedsilica or other suitable material) of the distal anchor 2404 can berelatively inflexible, e.g., relative to the dimensional variation ofthe optical fiber 2402 in response to the targeted environmentalpressure variations to be measured. In an illustrative example, anydimensional variation of the distal anchor 2404 can be less than orequal to 1/20, 1/100, or 1/1000 of any dimensional variation of apressure-sensing portion of the optical fiber 2402 measured in responseto the targeted environmental pressure variations, such as the pressurevariations that can be present in a percutaneous in vivo intravascularhuman blood pressure sensing application.

The tubular or other distal anchor 2404 can be attached to a hard,solid, or inelastic (e.g., fused silica) tubular or other housing 2406,such as by a soft, flexible, elastic, or compliant gasket 2408 that canbe located therebetween. A first sensing region 2410 of the opticalfiber 2402 can be securely captured, anchored, or affixed, to thehousing 2406, such as via a tubular or other attachment (e.g., hardenedepoxy or other adhesive) region 2412. A second sensing region 2414 ofthe optical fiber 2402 can be located within the housing 2406, such assuspended (e.g., freely or within a compliant material) between theencapsulator or attachment region 2412 and the hard distal anchor 2404.The suspended portion of the optical fiber 2402 can be installed orsecurely held longitudinally under tension. This can permit bothpositive and negative direction longitudinal displacement variations inthe suspended portion of the optical fiber 2402, which, in turn, canpermit sensing of both positive and negative environmental pressurevariations, as explained herein.

The gasket 2408 material (e.g., medical grade silicone) can berelatively more flexible, soft, elastic, or compliant than the housing2406 and than the distal anchor 2404, such as to allow longitudinaldimensional variation of gasket 2408 and the suspended second sensingregion 2414 of the optical fiber 2402 in response to the targetedenvironmental pressure variations to be measured, such as the pressurevariations that can be present in a percutaneous in vivo intravascularhuman blood pressure sensing application. The first sensing region 2410can be securely fixed to the hard housing 2406 by the encapsulator orattachment region 2412, while the second sensing region 2414 can besuspended within the hard housing 2406 and subject to longitudinaldimensional variation (along with longitudinal dimensional variation ofthe compliant gasket 2408). Therefore, the first sensing region 2410 canbe shielded from or made insensitive to environmental pressurevariations, but sensitive to environmental temperature variations, whilethe second sensing region 2414 can be sensitive to both environmentalpressure and temperature variations. In this way, light modulation inthe first sensing region 2410 due to temperature variations can bemeasured and used to compensate for or null-out the light modulationeffect of similar temperature variations experienced by the secondsensing region 2414 that is being used to measure environmental pressurevariations. In an illustrative example, the first sensing region 2410can include a first Fabry-Perot interferometer, and the second sensingregion 2414 can include a second Fabry-Perot interferometer. Theserespective interferometers can be written with different wavelengths.This can permit each interferometer to be individually separatelyaddressed by selecting a corresponding wavelength of light to provide tothe proximal end of the optical fiber 2402 to perform the selectiveindividual addressing of the interferometers.

FIG. 24 can be conceptualized as an arrangement in which at least oneoptical fiber sensing region can be suspended between two anchors (e.g.,hard tubes 2404, 2406) that can be separated from each other by acompliant region (e.g., gasket 2408) that can allow the anchoring tubes2404, 2406 (and hence the suspended portion of the optical fiber 2402)to experience longitudinal displacement in response to environmentalpressure variations. Based on finite element modeling (FEM) simulationanalysis and experimental laboratory data obtained from prototypes,corresponding to the arrangement illustrated in FIG. 24, a pressuresensitivity can be obtained that can be at least 100 to 150 times thepressure sensitivity of an optical fiber without such arrangement ofhard tubes 2404, 2406 separated from each other by the compliant gasket2408.

In an illustrative example, the entire pressure sensor assembly 2400 canbe less than or equal to 1.5 millimeters in length, such as less than orequal to 1.0 millimeter in length. The pressure sensor assembly 2400 canhave an outer diameter that can be less than or equal to 125micrometers. For comparison, 125 micrometers is the outer diameter of atypical single standard optical fiber as used in telecommunications. Thetubular housing 2406 can have an inner lumen diameter of about 50micrometers. In an example, the entire pressure sensor assembly 2400 canbe conveniently incorporated within a percutaneous or other guidewire,such as can be used for guiding an intravascular device (e.g., a stent,such as a coronary stent) to a desired location within a blood vessel.For example, the entire pressure sensor assembly 2400 can be includedwithin a solder or other joint of such a guidewire, such as betweenspring coils forming a body of the guidewire. Using fused silica orother glass components for all or portions of the tubular housing 2406or the fused silica distal anchor 2404 can provide components that canprovide a good matching of the temperature coefficient of expansion ofthese materials to the temperature coefficient of expansion of thematerial of the optical fiber 2402.

The arrangement shown in the illustrative example of FIG. 24 canadvantageously be durable, can be easy to make, can perform well such asin detecting and amplifying an environmental pressure variation, or canconsistently be made in a small form factor.

FIG. 25 shows an example of the pressure sensor assembly 2400 as it canbe prefinished and included or otherwise incorporated into apercutaneous intravascular guidewire assembly 2500. The guidewireassembly 2500 can include a core guidewire 2502, a flexible proximalspring coil region 2504 and a flexible distal spring coil region 2506that can terminate at a rounded and atraumatic distal tip. A generallycylindrical or other connector block 2508 can be included between andinterconnecting the proximal spring coil region 2504 and the distalspring coil region 2506. The connector block 2508 can include a reduceddiameter proximal end seat region 2510 and a reduced diameter distal endseat region 2512, about which windings of the flexible proximal springcoil region 2504 and a flexible distal spring coil region 2506 canrespectively be wound, such as with their outer circumferences flushwith an outer circumference of a midportion of the connector block 2508between the proximal end seat region 2510 and the reduced diameterdistal end seat region 2512. The connector block 2508 can provide ahousing for the pressure sensor assembly 2400. The optical fiber 2402can extend proximally from the pressure sensor assembly 2400 in theconnector block 2508 through the proximal spring coil region 2504, suchas to an optical connector at a proximal end of the guidewire assembly2500, where it can be optically coupled to optical, electronic, oroptoelectronic signal generation or processing circuitry. The coreguidewire 2502 of the guidewire assembly 2500 can bend or jog off of theconcentric longitudinal axis of the guidewire assembly 2500, such as ator near the connector block 2508, if needed to allow enough room for thepressure sensor assembly 2500 to be housed within the connector block2508 while also allowing passage of the core guidewire 2502 through theconnector block 2508 in such a lateral offset arrangement.

The connector block 2508 can provide a lateral axis portal 2514 that canbe located beyond a distal end region 2516 of the pressure sensorassembly 2400 such as to leave a distal end region 2516 of the pressuresensor assembly 2400 exposed to nearby environmental pressures to bemeasured, while providing a ceramic or other hard protectivecircumferential housing region that can protect the pressure sensorassembly 2400 from lateral pressure or lateral torque that may otherwiseinfluence the pressure sensor measurement to be obtained by longitudinalspatial variations of the pressure sensor assembly 2400.

FIG. 26 shows an example illustrating how components of the pressuresensor assembly 2400 can be integrated into or otherwise incorporatedinto a percutaneous intravascular guidewire assembly 2600. FIG. 26 issimilar to FIG. 25 in some respects, but in FIG. 26 the connector block2602 can provide a concentric axially aligned longitudinal passage forthe core guidewire 2502, such that it need not bend or jog as shown inFIG. 25. This can help preserve or utilize the mechanical properties orcharacteristics of the core guidewire 2502 or those of the guidewireassembly 2600. One or more components of the pressure sensor assembly2400 can be laterally offset from the concentric axially aligned coreguidewire 2502, such as within the connector block 2602. The connectorblock 2602 can include a lateral axis portal 2514. The distal anchor2404 and the gasket 2408 can be located in or near the lateral axisportal 2514, and can optionally be laterally recessed or otherwiseshielded from lateral pressure or torque that may otherwise influencethe pressure sensor measurement to be obtained by longitudinal spatialvariations of the integrated components of the pressure sensor assembly2400, such as explained above with respect to FIG. 25. The connectorblock 2602 can be constructed with a passage for the optical fiber 2402sized, shaped, or otherwise configured such as to provide a firstsensing region 2410 of the optical fiber 2402 that can be affixed to ahousing provided by the connector block 2602, such as explained herein.A second sensing region 2414 of the optical fiber 2402 can be suspendedwithin a housing provided by the connector block 2602, such as explainedherein. The optical fiber 2402 can extend outward from the connectorblock 2602 proximally, such as through the proximal spring coil region2504, such as with the optical fiber 2402 extending so as to belaterally offset from a longitudinal central axis of the guidewireassembly 2600.

FIG. 27 shows an example in which components of the pressure sensingassembly 2400 can be retrofitted to or otherwise integrated into anexisting guidewire assembly 2700, such as a RUNTHROUGH® guidewire,available from Terumo Kabushiki Kaisha, also known as Terumo Corp. Theguidewire assembly 2700 can include a proximal region 2702, that can beconstructed from a first material, such as stainless steel, and a distalregion 2706 that can be constructed from a second material, such asnitinol. Either or both of the proximal region 2702 and the distalregion 2704 can taper inward in a direction toward the distal end of theguidewire assembly 2700, such as in one or more tapering regions, whichcan be contiguous or separated by respective non-tapering regions. Adistal region 2706 of the guidewire assembly 2700 can include a proximalspring coil region 2504, a distal spring coil region 2506, a connectorblock 2708 (e.g., containing components of the pressure sensor assembly2400, such as described herein) therebetween from which a flattened orother core guidewire can extend distally toward and connecting to anatraumatic rounded distal tip 2710.

At least one groove 2712 can be formed on an outward circumferentialsurface of the guidewire assembly 2700. The groove 2712 can extend froma proximal end or region of the guidewire assembly 2700 toward and to adistal portion of the guidewire assembly 2700 and can terminate at aproximal side of the connector block 2708. The groove 2712 can extendalong all or a portion of the length of the guidewire assembly 2700,such as in a spiral helix or otherwise. The pitch of the helix can befixed or multi-valued (e.g., a looser pitch (e.g., between 30 mm and 50mm) at a proximal portion of the guidewire assembly 2700 and a tighterpitch (e.g., between 5 mm and 10 mm pitch) at the distal (e.g., over alength of about 30 centimeters) portion of the guidewire assembly 2700).The helical arrangement can help accommodate flexing curvature in theguidewire assembly 2700 as it is introduced along tortuous vascular orother non-linear paths. A tighter pitch can be more accommodating tocurvature in the guidewire assembly 2700. The groove 2712 can carry theoptical fiber 2402 therein, such as can be secured therein by anadhesive underlayer (e.g., UV-cured adhesive, hot-melt adhesive, epoxyor other two-part adhesive) or overlayer (e.g., such as any suitableovercoating used for an existing guidewire). In an example, the groove2712 can be about 40 micrometers across and about 40 micrometers deep,and can be constructed so as to only occupy about 1/100 or less of thesurface area of the guidewire assembly 2700, thereby leaving themechanical properties of the guidewire assembly 2700 substantiallyintact as though the groove 2712 were not present. For retrofitting anexisting guidewire, the groove 2712 can be formed by laser-etching orother suitable process. The guidewire can additionally or alternativelyformed together with the groove 2712, such as during drawing of theguidewire body during its manufacture, such as by mechanically scoringthe guidewire body or otherwise. If a portion of the guidewire body istapered down (e.g., toward a distal end, such as using centerless orother grinding), then any grooves that were formed during the guidewiredrawing, but removed by the grinding, can be replaced by a respectiveconnecting groove that can be formed after grinding, such as bylaser-etching the ground portion of the guidewire body.

FIG. 28 shows an example in which the pressure sensor assembly 2400(e.g., as explained herein) can be located at a distal end of aguidewire assembly 2800, e.g., more distal than the distal spring coilregion 2506, such as within or providing a rounded atraumatic distaltip. A flattened or other distal end of the core guidewire 2502 canconnect to a proximal end of the housing 2406 of the pressure sensorassembly 2400. More proximal regions of the guidewire assembly 2800 caninclude a proximal spring coil region 2504, a connector block (such as aconnector block 2508, which can optionally include a second, moreproximal pressure sensor as described with respect to FIG. 25), andother elements such as shown in FIG. 25.

The distal end pressure sensor assembly 2400 can include an anchoredfirst sensing region 2410 and a suspended second sensing region 2414,such as explained herein. The gasket 2408 and the distal anchor 2404 canbe located within a cylindrical or other recess 2802 that can be exposedto the ambient environment about the distal end of the guidewireassembly 2800. In an example such as shown in FIG. 28, the recess 2802can be cylindrical and can extend longitudinally along the central axisof the guidewire assembly 2800, such as to face longitudinally outwardfrom the distal end of the guidewire assembly 2800. In an example, thedistal end of the optical fiber 2402 can be attached to the anchor 2404,and both the anchor 2404 and the gasket 2408 can be suspended within therecess 2802, such as by tension in the optical fiber 2402 to which theanchor 2404 can be attached with the gasket 2408 captured proximal tothe anchor 2404. This can help provide pressure sensing due tolongitudinal optical fiber tension variations near the distal end of theguidewire assembly 2800, and can help isolate the effect of lateralpressure variations or torque upon the pressure sensor assembly 2400.

Having a pressure sensor located at a guidewire distal tip can provideadvantages in certain applications, such as where information aboutpressure distal to an occlusion may be desirable. For example, whenpushing a guidewire across a chronic total vascular occlusion, it may bedifficult to determine whether the distal tip is within a lumen of theblood vessel or within a subintimal layer of the blood vessel. Adistal-tip pressure sensor can permit providing distal-tip pressureinformation that can be useful in determining the nature of suchlocation of the distal tip of the guidewire assembly 2800. In an examplein which a distal tip pressure sensor is provided together with a moreproximal pressure sensor (e.g., located between the proximal spring coilregion 2504 and the distal spring coil region 2506), a pressuredifferential across an occlusion can be sensed and provided to a user,such as for diagnostic or interventional (e.g., stent-placement)purposes.

FIG. 29 shows an example of a proximal region of a guidewire assembly2900, such as one of the various guidewire assemblies described herein,terminating at a proximal end connector 2902. The guidewire assembly2900 can include a helically wound optical fiber 2402 that can belocated in a helical groove 2712 along the guidewire body. The proximalend connector 2902 can include separable portions: (1) a distal portionthat can include a metal or other tube 2904 (also referred to as atubular coupler) having an interior lumen diameter that can be attachedto both the outer diameter of the body of the proximal region of theguidewire assembly 2900 and the outer diameter of a ceramic or otherdistal ferrule 2906 such that the optical fiber can extend from aperiphery of the guidewire body to and through a center axis lumen ofthe distal ferrule 2906; and (2) a proximal portion that can include aconnector housing 2908 carrying a ceramic or other proximal ferrule2910, a split sleeve ferrule guide 2912, and a distal receptacle guide2914 that can provide a tapered portion into which a portion of thedistal ferrule 2906 and the metal tube 2904 can be received. The opticalfiber 2402 can terminate at a flat or dome polished (e.g., ultrapolishedphysical connector, “UPC”) proximal end of the distal ferrule 2906,where it can butt against and optically couple with a flat or domepolished (e.g., UPC) distal end of the proximal ferrule 2910, which canprovide a center axis lumen through which an optical fiber 2402 canextend in a proximal direction, such as to an optical, electronic, oroptoelectronic signal generation or processing apparatus. While theoptical fibers 2402 and 2916 can be the same diameter, in an example,the optical fiber 2402 can be a small diameter optical fiber (e.g., 25micrometers outer diameter) and the optical fiber 2916 can be a standardsized telecommunications optical fiber (e.g., 125 micrometers outerdiameter), such as with the mode field diameter (MFD) of the opticalfiber 2402 being less than or equal to the MFD of the optical fiber2916. When the proximal end of the guidewire terminating in connectorportion 2902 is detached, other components can be easily slipped overthe guidewire.

Using various techniques described above, changes in ambient pressurecan be detected by measuring the wavelength change, e.g., quantifiedchange in phase-shift, by an FBG sensor within a housing, e.g., housing308 of FIG. 3. As described above with respect to FIGS. 4A-4C and FIG.6A, the change in phase-shift can be quantified by locking a laser at aposition on a slope of the transmission notch of the resonant feature,tracking a particular optical power level in the resonant feature, andadjusting the bias current of the laser which, in turn, subtly changesthe wavelength to maintain this “locked” relationship.

These techniques can produce satisfactory results when the opticalinsertion loss is constant. In some example implementations, however,the overall insertion loss of the pressure sensor and/or system canchange during the measurement, e.g., kinking in the optical fiber. Asshown and described below with respect to FIG. 30, a change in theoptical insertion loss can lead to an artificial shift in the trackingwavelength, and thus an offset error in the pressure reading, if theoptical locking level or threshold is not adjusted accordingly.

FIG. 30 depicts a conceptual response diagram illustrating the effect ofan uncorrected locking level on a locking wavelength. In FIG. 30, wherethe x-axis represents wavelength and the y-axis represents the intensityof the reflected light, a transmission notch 3000 is shown within areflection band 3002, and a reduced reflection band 3004, which iscaused by insertion loss. An initial locking level, or opticalthreshold, 3006 is depicted, which corresponds to a wavelength of about1550.85 nm and a reflection intensity of 50%.

If insertion loss is introduced, which results in the reduced reflectionband 3004, then the locking level may move up or down the slope of thereduced reflection band 3004 in order to maintain its locking level,e.g., 50%, despite the fact that the transmission notch 3004 has notmoved. If the insertion loss increases (optical power decreases), thenthe shift can be to a higher, incorrect locking wavelength because thelocking circuit climbs the slope of the reduced reflection band 3004 tomaintain the set optical level, as shown at 3008. If the insertion lossdecreases (optical power increases)(not depicted in FIG. 30), then theshift can be to a lower, incorrect locking wavelength because thelocking circuit moves down the slope of the reduced reflection band 3004to maintain the set optical power level. Either of these conditions canlead to a significant drift in the apparent pressure level even if therehas been no phase-shift change in the FBG filter.

As described in more detail below, using various techniques of thisdisclosure, the locking level 3006 can be corrected for insertion loss,resulting in a corrected locking level 3010. In accordance with thisdisclosure, a small dither signal can be added to the wavelength of thelaser at, for example, a frequency outside those associated with thepressure sensing. Then, the AC component, which is the change in theoptical signal reflected from the pressure sensor back to the opticaldetector, e.g., optical detector 608 of FIG. 6A, can be extracted fromthe optical signal via an electronic circuit associated with the opticaldetector. The magnitude of the AC component can then be used to make anyadjustments to the locking level to null out any offset errors.

FIG. 31 depicts the conceptual response diagram of FIG. 30 compensatedfor optical insertion loss in an optical pressure sensor using varioustechniques of this disclosure. In FIG. 31, where the x-axis representswavelength and the y-axis represents the intensity of the reflectedlight, a transmission notch 3000 is shown within a reflection band 3002,and a reduced reflection band 3004, which is caused by insertion loss.

Two AC components 3012, 3014 are depicted in FIG. 31, where the ACcomponent 3012 depicts a magnitude of the AC component with no excessloss and where the AC component 3014 depicts a magnitude of the ACcomponent with excess loss. Thus, the magnitude of the AC component canchange with insertion loss.

As indicated above, a small dither signal 3016 can be added to thewavelength of the laser. Then, an AC component can be extracted from theoptical signal via an electronic circuit associated with the opticaldetector. As can be seen in FIG. 31, the amplitude of the AC components3012, 3014 can vary in proportion to the overall signal level as long asthe amount of wavelength dither is held constant. That is, if thewavelength range of the dither 3016 is held constant, the magnitude ofthe AC component can scale directly with the optical insertion loss.

By comparing a current value of the AC component, e.g., AC component3014, to an initial value of the AC component, e.g., AC component 3012,the controller 602 (FIG. 6A) can determine whether the optical insertionloss has increased or decreased. The current value of the AC componentcan be fed back to the optical locking circuit of FIG. 6A, a portion ofwhich is described below with respect to FIG. 33. Then, because the ACcomponent is reduced in proportion to the change in insertion loss, thecontroller 602 of FIG. 6A can adjust the optical locking levelaccordingly to maintain the correct locking wavelength.

In some examples, a frequency and amplitude of the wavelength dither3016 can be selected so as to be compatible with the pressuremeasurements. For example, for the dither frequency, a value can beselected that is higher than the necessary bandwidth for pressuresensing. Assuming, for example, that the pressure bandwidth is between0-25 Hz, then it might be desirable to select a frequency for thewavelength dither at least five times higher than the pressurebandwidth.

FIG. 32 is a flow diagram illustrating an example of a method 3200 forcompensating for optical insertion loss in an optical pressure sensorusing various techniques of this disclosure. The controller 602 of FIG.6A can establish, or determine, an optical locking level with no excessinsertion loss (3202), e.g., initial locking level 3006 of FIG. 31, andestablish, or determine, an initial amplitude of a dither signal (3204),e.g., the AC component 3012 of FIG. 31, by extracting the dither signalfrom the optical signal reflected from the pressure sensor and measuringits amplitude. The controller 602 can measure a new amplitude of thedither signal (3206), e.g., the AC component 3014 and compare the newamplitude to the initial amplitude (3208). If the insertion loss haschanged (“YES” branch of 3210), as determined by the comparison at 3208,then the controller 602 can control either the laser drive currentcontrol 614 of FIG. 6A or the locking set point value 612 of FIG. 6A toadjust the locking level to a new value (3212), e.g., if the ACcomponent decreases then the locking level is reduced by the appropriateamount. If the insertion loss has not changed (“NO” branch of 3210), asdetermined by the comparison at 3208, then the controller 602 cancontinue to measure the new amplitude of the dither signal at 3206.

FIG. 33 is a block diagram of an example of a portion of the lasertracking system of FIG. 6A for compensating for optical insertion lossin an optical pressure sensor using various techniques of thisdisclosure, in accordance with this disclosure. An AC dither generator3312 generates a dither signal that is summed together with the lasercontrol current via summer 3314 and passed to the laser current drivecircuit 614. The laser current drive circuit 614 generates a drivecurrent for laser 604 of FIG. 6A.

An optical signal reflected back from the pressure sensor, e.g.,pressure sensor 300 of FIG. 3, is detected by the optical detector 608,amplified by electrical amplifier 3300, and filtered by a low passfilter 3302, e.g., frequencies of about 0-25 Hz, and a high pass filter3304, e.g., frequencies greater than 25 Hz. The low pass filter 3302passes the DC level to a locking comparator 3306 and the high passfilter 3304 passes the high pass filtered signal, or AC component, tothe controller 602, which measures the amplitude of the dither signal(3308), or AC component, and calculates the optical locking level(3310), e.g., if the AC component decreases then the locking level isreduced to the appropriate value. The controller 602 passes thecalculated optical locking level to the locking comparator 3306, whichcompares the DC level and the calculated optical locking level. Thelaser current drive circuit 614 or the locking set point 612 can beadjusted based on the comparison. In this manner, a constant centerwavelength is maintained.

In one example implementation, the frequency of the dither 3016 of FIG.31 can be selected in order to design a low-pass filter 3302 that canreduce the residual AC dither component in the electrical path to thelocking circuit controlled by the laser current drive circuit 614. Thismay be desirable in order to prevent the locking circuit from chasingthe locking level at the frequency of the dither. It may be desirablefor the locking circuit to see the average or DC level of the opticallocking level.

There are many ways to filter the optical signal and only one example ispresented in this disclosure. Other filtering techniques or techniquesfor suppressing the AC component could be employed and are consideredwithin the scope of this disclosure.

In order to ensure that the laser is able to respond to the ditherfrequency chosen without any reduction in the actual wavelength shiftdesired, there may be factors to consider in selecting a ditherfrequency. For example, it has been found that the design of the lasersubmount has an effect on the frequency at which the laser can ditherthe laser.

Typical dither frequencies can range from around 100 Hz to 1000 Hzbefore the response starts to diminish. In one example implementation,it may be desirable to select a dither frequency between about 300 Hzand about 10400 Hz.

The dither magnitude can be selected to have an appropriate scale togive a detectable AC component, e.g., around ±10% of the overall DCsignal level. In this example, if the maximum optical power level isassumed to be about 1000 μW and the slope is assumed to be about 50μW/pm, then it may be desirable to shift the wavelength of the laser bythe equivalent of about ±2 pm (±1000 μW). If the laser is assumed tohave a wavelength coefficient of about 5 pm/mA, then this would equateto a bias current dither of about ±0.4 mA. These numbers are given forpurposes of illustration only and could be adjusted within sensiblelimits.

To summarize, with respect to FIGS. 31-33, this disclosure describes,among other things, the following techniques: compensating for changesin optical insertion loss of the pressure sensor that would otherwise beseen as large drifts in the apparent measured pressure; calculating andadjusting an optical locking level to achieve compensation of changes inoptical insertion loss by wavelength dithering of the tracking laser;applying wavelength dither to a tracking laser to generate a signal withamplitude proportional to optical insertion loss; and applying feedbackto an optical locking level to compensate optical insertion loss.

It should be noted that the dither techniques described above can beused in a similar manner to track the insertion loss of an intravascularultrasound (IVUS) imaging device and to make adjustments to the opticallocking levels. It may also be desirable to make dynamic adjustments toa sensitivity correction matrix for the imaging elements in a receivemode. The quality of imaging can be improved when the sensitivity of theelements are balanced in the reconstruction matrix to reduce side-lobelevels.

A first order calibration of the receive sensitivity of the elements canbe made by measuring the AC component from the wavelength dither as thisindicates the slope of the sensing element. The expected receiveultrasound signal is proportional to the ultrasound energy imparted onthe element (this is converted to a change in the optical cavity lengthor phase-shift) multiplied by the slope of the cavity. Therefore, byknowing the slope from the dither, an expected signal sensitivity fromthe element can be calculated.

In the case of IVUS, the relationship of the frequencies is reversed,where the dither frequency is well below the ultrasound frequencies andis filtered out by the ultrasound electrical circuits.

To summarize, with respect to IVUS imaging devices, this disclosuredescribes, among other things, the following techniques: dynamicallyadjusting optical locking levels; dynamically adjusting an elementcalibration matrix to improve image reconstruction; and calibratingreceive sensitivity of elements based on dither slope measurements. Manyof the techniques described in this disclosure are applicable tointravascular imaging devices, such as those described in Bates & VardiU.S. Pat. Nos. 7,245,789, 7,447,388, 7,660,492, 8,059,923, U.S. Pat.Pub. No. US-2012-0108943-A1, and U.S. Provisional Patent Application No.61/783,716, titled “Optical Fiber Ribbon Imaging Guidewire and Methods”to Tasker et al. and filed on Mar. 14, 2013, each of which is herebyincorporated by reference herein in its entirety.

Turning to another aspect, in any optical system with highly coherentlight sources, e.g., a narrow linewidth laser, there is a possibilitythat any unintended reflections, even very weak ones, can form aresonant optical cavity within the device. The cavity can exhibit astrong frequency component that depends on the optical path length ofthe cavity (in this case the length of optical fiber between reflectionpoints). The frequency of the cavity is given by:

${\Delta\; v} = \frac{C}{2\; L}$where Δv=frequency separation of maxima (Hz), C=speed of light, andL=optical path length (Length×refractive index). The longer the cavity,the more closely spaced the ripples in the frequency and wavelengthdomains.

A large amount of optical energy can be circulated within the pressuresensing device and, under certain conditions, can form undesirableoptical resonances with other elements of the system. The undesirableresonances can be formed between any two points of optical reflection.For instance, the undesirable resonances can be formed between the FBGsand a system connector, or the FBGs and a pressure wire connector. Inaccordance with this disclosure and as described in more detail belowwith respect to FIGS. 34-37, these undesirable resonances can beaveraged out using dither techniques, thereby reducing their overalleffect on the pressure measurements.

FIG. 34 depicts a conceptual response diagram illustrating undesirableoptical resonances caused by additional reflection in an optical system.In FIG. 34, where the x-axis represents wavelength and the y-axisrepresents the intensity of the reflected light, a transmission notch3400 is shown within a reflection band 3402. The undesirable opticalresonances are shown as ripples 3404 overlaid on the fundamentalresponse. In this example the undesirable reflection point is at adistance of about 70 mm from the FBGs.

In an example of a pressure sensing device, there may be an opticalconnector to the system about two meters from the FBG filters that is apossible source of reflections. The calculated expected wavelength ofthe ripple caused by a reflection at two meters is approximately 0.4 pm(at 1550 nm). There is a possibility that the locking system can becomeconfused by these ripples 3404 and hop between them, which appears as asudden jump in the apparent pressure reading, e.g., 10 mm/Hg, shown anddescribed below with respect to FIG. 35. In the context of pressuresensing, such a jump is unwanted and likely unacceptable due to the needfor accurate pressure measurements.

FIG. 35 depicts the conceptual response diagram of FIG. 34 furtherillustrating undesirable locking circuit wavelength hopping. FIG. 35shows a calculated response for a weak reflection at 70 mm (anon-limiting example for purposes of illustration only) and how thelocking circuit can become confused and shift to a different wavelength.More particularly, the locking circuit can become confused because theoptical locking level 3504 can intersect both the fundamental response3402 (at point 3506) and a ripple 3404 (at point 3508), resulting in twopossible optical locking wavelengths. As a result of the ripple 3404,the desired optical locking wavelength at 3500 can jump to a higheroptical locking wavelength 3502. Assuming that the sensor has apressure-to-wavelength coefficient of around 1 pm for 25 mm/Hg and thatthe 2 m cavity has a ripple period of 0.4 pm, then the apparent shift isapproximately 10 mm/Hg, which is highly undesirable.

In accordance with this disclosure and as described in more detail belowwith respect to FIG. 36, the optical dither techniques described abovecan be used to average through these ripples 3404 and to reduce oreliminate their effects on determining an optical locking wavelength.

FIG. 36 depicts the conceptual response diagram of FIG. 35 compensatedfor optical cavity noise using various techniques of this disclosure. Inaccordance with this disclosure, optical wavelength dither (describedabove) can be used to sweep or average through a number of the rippleperiods. Examples of lower and upper bounds of the dither opticalwavelength are depicted at 3600, 3602, respectively. In the exampleshown in FIG. 36, within the lower and upper wavelength bounds 3600,3602 are four ripples 3404 that can be averaged. Less or more ripplescan be averaged.

When the laser wavelength is dithered, e.g., at a frequency at leastfive times the bandwidth of the pressure signal, the high frequency ACcomponent can be extracted from the optical signal by filtering, similarto what was described above with respect to the insertion losscompensation techniques and as depicted in FIG. 33. If the pressuresignal has a bandwidth of about 0-25 Hz, then the dither frequency is atleast 125 Hz, for example. In other examples, the dither frequency isabout 300-400 Hz.

Once the high frequency AC component is extracted, then the controller602 of FIG. 6 can average the AC component over the region of interest,e.g., over four ripples 3404 as in FIG. 36. The dithering occurs at afaster rate than the rate at which the ripples 3404 move side to sideduring the measurement. As a result, the controller 602 can averagethrough the ripples 3404, thereby removing the optical cavity noise. Thecontroller 602 can then determine an optical locking level andwavelength without becoming confused and jumping to an incorrect opticallocking wavelength.

The amplitude and frequency requirements of the dither wavelength can bemade to complement the insertion loss compensation (described above),e.g., a frequency of about 300-400 Hz. The amplitude of the wavelengthdither can be calculated based on the wavelength separation of theundesirable ripples. In one example, it may be desirable to dither by awavelength amount that would encompass a sufficient number of ripples togive satisfactory averaging. If the ripples are more closely spaced,then the controller 602 can control generation of a relatively smalleramount of dither than if the ripples were more widely spaced to achievethe same amount of averaging. Take, for example, a two meter longdistance between the reflection points, the calculated wavelength of theripple caused by a reflection at two meters is approximately 0.4 pm (at1550 nm), then it may be desirable to dither the wavelength of the laserby 5 ripple periods to give satisfactory averaging. The wavelength ofthe laser can be dithered by a total of 2 pm (0.4 pm×5 ripples). Thiscorresponds to a dither in the laser current of around 0.4 mA, where atypical laser is 5 pm/mA.

In one example implementation, the same dither frequency and electricalfiltering used for the insertion loss compensation techniques describedabove can be used to compensate for the optical cavity noise to allowthe usual detection of the pressure readings in the 0-25 Hz bandwidth.In some example implementations, the low frequencies, e.g., 0-25 Hz,that correspond to the pressure signals can be used to control thelocking circuit in order to reduce the confusion presented by individualripples. In one example, the electrical filter circuits can be used topresent the average optical detector value to the locking circuits, thusreducing the discrete step nature of the individual ripples.

FIG. 37 depicts a flow diagram illustrating an example of a method 3700for compensating for optical cavity noise in an optical pressure sensorusing various techniques of this disclosure. In FIG. 37, the controller602 of FIG. 6 can control the laser 604 to generate a dither signal at afrequency outside of the range associated with a pressure signal (3702).For example, for a pressure signal having a bandwidth of about 0-25 Hz,the dither frequency can be at least 125 Hz. In one specific example,the dither frequency can be about 300-400 Hz. Next, the optical detector608 of FIG. 6A can receive the reflected optical signal from thepressure sensor (3704). A low pass filter, e.g., filter 3302 of FIG. 33,can remove or suppress the AC component at the dither signal frequency(3706). Then, the controller 602 can determine a low frequency value,e.g., the average locking level in the low frequency band (0-25 Hz),over the specified region of interest of the signal, e.g., over fourripples (3708). Finally, the controller 602 can determine a noisecompensated optical locking wavelength based on the determined averagelow frequency value (3710).

Using the one or more techniques such as disclosed above, the presentapplicant has described an optical pressure sensing guidewire suitablefor delivery within a body lumen of a patient, e.g., for diagnosticassessment of coronary obstructions. This can advantageously optionallyprovide temperature compensation for sensing pressure within a bodylumen. In addition, the present subject matter can advantageouslymechanically enhance the sensitivity of the fiber to pressure, such aswith an extrinsic arrangement. Further, the present subject matter canutilize Fiber Bragg Gratings in the miniaturized optical fiber therebyresulting in a cost effective and manufacturable design.

Each of these non-limiting examples described above can stand on itsown, or can be combined in various permutations or combinations with oneor more of the other examples.

The above detailed description includes references to the accompanyingdrawings, which form a part of the detailed description. The drawingsshow, by way of illustration, specific embodiments in which theinvention can be practiced. These embodiments are also referred toherein as “examples.” Such examples can include elements in addition tothose shown or described. However, the present inventors alsocontemplate examples in which only those elements shown or described areprovided. Moreover, the present inventors also contemplate examplesusing any combination or permutation of those elements shown ordescribed (or one or more aspects thereof), either with respect to aparticular example (or one or more aspects thereof), or with respect toother examples (or one or more aspects thereof) shown or describedherein.

In the event of inconsistent usages between this document and anydocuments so incorporated by reference, the usage in this documentcontrols.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherinstances or usages of “at least one” or “one or more.” In thisdocument, the term “or” is used to refer to a nonexclusive or, such that“A or B” includes “A but not B,” “B but not A,” and “A and B,” unlessotherwise indicated. In this document, the terms “including” and “inwhich” are used as the plain-English equivalents of the respective terms“comprising” and “wherein.” Also, in the following claims, the terms“including” and “comprising” are open-ended, that is, a system, device,article, composition, formulation, or process that includes elements inaddition to those listed after such a term in a claim are still deemedto fall within the scope of that claim. Moreover, in the followingclaims, the terms “first,” “second,” and “third,” etc. are used merelyas labels, and are not intended to impose numerical requirements ontheir objects.

Method examples described herein can be machine or computer-implementedat least in part. Some examples can include a computer-readable mediumor machine-readable medium encoded with instructions operable toconfigure an electronic device to perform methods as described in theabove examples. An implementation of such methods can include code, suchas microcode, assembly language code, a higher-level language code, orthe like. Such code can include computer readable instructions forperforming various methods. The code may form portions of computerprogram products. Further, in an example, the code can be tangiblystored on one or more volatile, non-transitory, or non-volatile tangiblecomputer-readable media, such as during execution or at other times.Examples of these tangible computer-readable media can include, but arenot limited to, hard disks, removable magnetic disks, removable opticaldisks (e.g., compact disks and digital video disks), magnetic cassettes,memory cards or sticks, random access memories (RAMs), read onlymemories (ROMs), and the like.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described examples (or one or moreaspects thereof) may be used in combination with each other. Otherembodiments can be used, such as by one of ordinary skill in the artupon reviewing the above description. The Abstract is provided to complywith 37 C.F.R. § 1.72(b), to allow the reader to quickly ascertain thenature of the technical disclosure. It is submitted with theunderstanding that it will not be used to interpret or limit the scopeor meaning of the claims. Also, in the above Detailed Description,various features may be grouped together to streamline the disclosure.This should not be interpreted as intending that an unclaimed disclosedfeature is essential to any claim. Rather, inventive subject matter maylie in less than all features of a particular disclosed embodiment.Thus, the following claims are hereby incorporated into the DetailedDescription as examples or embodiments, with each claim standing on itsown as a separate embodiment, and it is contemplated that suchembodiments can be combined with each other in various combinations orpermutations. The scope of the invention should be determined withreference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

The claimed invention is:
 1. An apparatus comprising: an elongatedassembly, at least a portion of which is sized, shaped, or otherwiseconfigured to be inserted into a human body to measure a pressure at aninternal location within the human body, wherein the elongated assemblyincludes: a guidewire including a solid core wire having an outersurface, a portion of the outer surface comprising a groove directly onthe outer surface of the guidewire; an optical fiber positioned withinthe groove and extending longitudinally along the guidewire, the opticalfiber configured to communicate light between a location outside of thehuman body and a portion of the optical fiber that is to be located ator near the internal location within the human body at which thepressure is to be measured; at least one optical fiber pressure sensorcoupled to the optical fiber and configured to be located on theguidewire to allow positioning at or near the internal location withinthe human body at which pressure is to be measured; and an imagingsensor configured to be located on the guidewire and configured to imagea region at or near the internal location within the human body and todetect a responsive imaging signal for communication via the guidewireto the location outside of the human body for processing into an imageof the region, wherein the optical fiber pressure sensor comprises: afirst optical fiber anchor, to which a first portion of the opticalfiber is secured; a second optical fiber anchor, to which a secondportion of the optical fiber is secured; and a gasket longitudinallyarranged between the first and second anchors and including a passagethrough which a third portion of the optical fiber passes, the gasketbeing more elastic or compliant than the first and second anchors; andwherein the first and second anchors and the gasket are arranged to usethe elastic or compliant nature of the gasket to allow at least one oflongitudinal stretching or compression of the optical fiber between thefirst and second anchors to sense pressure at the internal locationwithin the human body.
 2. The apparatus of claim 1, wherein the grooveis sized for and carries only one optical fiber, and wherein the onlyone optical fiber has a diameter of between 25 micrometers and 30micrometers, inclusive.
 3. The apparatus of claim 1, wherein the opticalfiber extends within the groove helically along at least a portion of alength of the core wire.
 4. The apparatus of claim 1, wherein the atleast one optical fiber pressure sensor comprises two or more opticalfiber pressure sensors that are configured to operate at differentwavelengths.
 5. The apparatus of claim 1, wherein the optical fiberpressure sensor comprises a compliant sensor membrane configured tomechanically couple received pressure toward a Fiber Bragg Gratinginterferometer.
 6. The apparatus of claim 1, wherein the optical fiberis arranged under longitudinal tension between the first and secondanchors.
 7. The apparatus of claim 1, wherein the elongated assemblyincludes a spring coil arranged coaxially to a longitudinal axis of theelongated assembly, and comprising a connector block coupled to thespring coil, the connector block including the optical fiber pressuresensor arranged with the compliant gasket exposed to receive an ambientpressure at the internal location within the human body.
 8. Theapparatus of claim 1, wherein the guidewire includes a jog toaccommodate the optical fiber pressure sensor.
 9. The apparatus of claim1, wherein the optical fiber pressure sensor is located at a distal tipof the guidewire.
 10. The apparatus of claim 1, comprising a splitsleeve ferrule holding and concentrically aligning at least a portion ofa distal guide ferrule against a portion of a proximal guide ferrule.11. The apparatus of claim 1, comprising: a coil disposed about at leasta portion of the guidewire.
 12. The apparatus of claim 1, wherein theimaging sensor includes: an optical fiber ribbon having a plurality ofoptical fibers disposed about the core wire of the guidewire; and aplurality of imaging gratings to couple light into and/or out of one ormore respective optical fibers of the optical fiber ribbon.
 13. Theapparatus of claim 1, wherein the at least one optical fiber pressuresensor comprises a Fiber Bragg Grating (FBG) interferometer.
 14. Theapparatus of claim 13, wherein the FBG interferometer comprises at leasttwo Fiber Bragg Gratings, wherein the at least two Fiber Bragg Gratingsare arranged or otherwise configured to permit optically discriminating,at or near the internal location within the human body at which pressureis to be measured, between a change in pressure and a change intemperature.
 15. The apparatus of claim 1, further comprising an opticalfiber ribbon comprising a plurality of optical fibers, the optical fiberribbon disposed about the outer surface of the guidewire.
 16. Theapparatus of claim 15, comprising a plurality of imaging gratingsconfigured to couple light into or out of one or more respective opticalfibers of the ribbon.
 17. An apparatus comprising: an elongatedassembly, at least a portion of which is sized, shaped, or otherwiseconfigured to be inserted into a human body to measure a pressure at aninternal location within the human body, wherein the elongated assemblyincludes: a guidewire including a solid core wire having an outersurface, a portion of the outer surface comprising a groove directly onthe outer surface of the guidewire; an optical fiber positioned withinthe groove and extending longitudinally along the guidewire, the opticalfiber configured to communicate light between a location outside of thehuman body and a portion of the optical fiber that is to be located ator near the internal location within the human body at which thepressure is to be measured; at least one optical fiber pressure sensorcoupled to the optical fiber and configured to be located on theguidewire to allow positioning at or near the internal location withinthe human body at which pressure is to be measured; and an imagingsensor configured to be located on the guidewire and configured to imagea region at or near the internal location within the human body and todetect a responsive imaging signal for communication via the guidewireto a location outside of the human body for processing into an image ofthe region, wherein the optical fiber is a first optical fiber having aproximal end connector, the proximal end connector configured to becoupled to a proximal end of the guidewire, the proximal end connectorcomprising: a distal portion comprising: a tube defining an interiorfirst passage that is sized and shaped to receive the proximal end ofthe guidewire; a distal guide ferrule, at least a portion of whichdefines a transitional interior second passage that is sized and shapedto allow the optical fiber to be transitionally routed from an outercircumferential periphery of the proximal end of the guidewire to a morelongitudinally central location toward a proximal end of the distalguide ferrule; and a proximal portion comprising: a proximal guideferrule, including a lumen sized and shaped for passing a second opticalfiber having a larger diameter than the first optical fiber, wherein thedistal and proximal portions are user-attachable to bring the first andsecond optical fibers into concentric longitudinal alignment with eachother.
 18. The apparatus of claim 17, wherein the groove is sized forand carries only one optical fiber, and wherein the only one opticalfiber has a diameter of between 25 micrometers and 30 micrometers,inclusive.
 19. The apparatus of claim 17, wherein the optical fiberextends within the groove helically along at least a portion of thelength of the core wire.
 20. The apparatus of claim 17, wherein theimaging sensor includes: an optical fiber ribbon having a plurality ofoptical fibers disposed about the core wire of the guidewire; and aplurality of imaging gratings to couple light into and/or out of one ormore respective optical fibers of the optical fiber ribbon.
 21. Theapparatus of claim 17, wherein the at least one optical fiber pressuresensor comprises two or more optical fiber pressure sensors that areconfigured to operate at different wavelengths.
 22. The apparatus ofclaim 17, wherein the guidewire includes: a proximal portion and adistal portion; and a mechanical joint to join the proximal portion tothe distal portion.
 23. The apparatus of claim 22, further comprising:an optical fiber ribbon comprising a plurality of optical fibers, theoptical fiber ribbon disposed about the outer surface of the guidewire,wherein the plurality of optical fibers includes 32 optical fibers. 24.The apparatus of claim 17, wherein the at least one optical fiberpressure sensor comprises a Fiber Bragg Grating (FBG) interferometer.25. The apparatus of claim 24, wherein the FBG interferometer comprisesat least two Fiber Bragg Gratings, wherein the at least two Fiber BraggGratings are arranged or otherwise configured to permit opticallydiscriminating, at or near the internal location within the body atwhich pressure is to be measured, between a change in pressure and achange in temperature.
 26. The apparatus of claim 17, further comprisingan optical fiber ribbon comprising a plurality of optical fibers, theoptical fiber ribbon disposed about an outer surface of the elongatedassembly.
 27. The apparatus of claim 26, comprising a plurality ofimaging gratings configured to couple light into or out of one or morerespective optical fibers of the optical fiber ribbon.